fix(ptx): downgrade yawning/obfs4

It seems the version of obfs4 we're using introduces a regression as
explained at ooni/probe#1986.

I'm working with @ainghazal to fix this issue in the master branch
of this repository. Our understanding is that the elligator algorithm
changed in obfs4, bringing in significant improvements. But we could
also bisect the issue to such an improvement. So, it may be that some
back and forth is required to settle the issue.

For the purpose of this release branch, thus, I've just downgraded
to a previous version to see if this fixes the issue.

Reference issue: ooni/probe#2016.

go.mod

@@ -48,7 +48,7 @@ require (
 	github.com/tjfoc/gmsm v1.4.1 // indirect
 	github.com/xtaci/smux v1.5.16 // indirect
 	github.com/ziutek/mymysql v1.5.4 // indirect
-	gitlab.com/yawning/obfs4.git v0.0.0-20220102012252-cbf3f3cfa09c
+	gitlab.com/yawning/obfs4.git v0.0.0-20210511220700-e330d1b7024b
 	gitlab.com/yawning/utls.git v0.0.12-1
 	golang.org/x/crypto v0.0.0-20220112180741-5e0467b6c7ce // indirect
 	golang.org/x/net v0.0.0-20220114011407-0dd24b26b47d

go.sum

@@ -9,8 +9,6 @@ dmitri.shuralyov.com/state v0.0.0-20180228185332-28bcc343414c/go.mod h1:0PRwlb0D
 filippo.io/age v1.0.0 h1:V6q14n0mqYU3qKFkZ6oOaF9oXneOviS3ubXsSVBRSzc=
 filippo.io/age v1.0.0/go.mod h1:PaX+Si/Sd5G8LgfCwldsSba3H1DDQZhIhFGkhbHaBq8=
 filippo.io/edwards25519 v1.0.0-rc.1/go.mod h1:N1IkdkCkiLB6tki+MYJoSx2JTY9NUlxZE7eHn5EwJns=
-filippo.io/edwards25519 v1.0.0-rc.1.0.20210721174708-390f27c3be20 h1:iJoUgXvhagsNMrJrvavw7vu1eG8+hm6jLOxlLFcoODw=
-filippo.io/edwards25519 v1.0.0-rc.1.0.20210721174708-390f27c3be20/go.mod h1:N1IkdkCkiLB6tki+MYJoSx2JTY9NUlxZE7eHn5EwJns=
 git.apache.org/thrift.git v0.0.0-20180902110319-2566ecd5d999/go.mod h1:fPE2ZNJGynbRyZ4dJvy6G277gSllfV2HJqblrnkyeyg=
 git.torproject.org/pluggable-transports/goptlib.git v0.0.0-20180321061416-7d56ec4f381e/go.mod h1:YT4XMSkuEXbtqlydr9+OxqFAyspUv0Gr9qhM3B++o/Q=
 git.torproject.org/pluggable-transports/goptlib.git v1.0.0/go.mod h1:YT4XMSkuEXbtqlydr9+OxqFAyspUv0Gr9qhM3B++o/Q=
@@ -771,11 +769,9 @@ github.com/ziutek/mymysql v1.5.4 h1:GB0qdRGsTwQSBVYuVShFBKaXSnSnYYC2d9knnE1LHFs=
 github.com/ziutek/mymysql v1.5.4/go.mod h1:LMSpPZ6DbqWFxNCHW77HeMg9I646SAhApZ/wKdgO/C0=
 gitlab.com/yawning/bsaes.git v0.0.0-20190805113838-0a714cd429ec h1:FpfFs4EhNehiVfzQttTuxanPIT43FtkkCFypIod8LHo=
 gitlab.com/yawning/bsaes.git v0.0.0-20190805113838-0a714cd429ec/go.mod h1:BZ1RAoRPbCxum9Grlv5aeksu2H8BiKehBYooU2LFiOQ=
-gitlab.com/yawning/edwards25519-extra.git v0.0.0-20211229043746-2f91fcc9fbdb h1:qRSZHsODmAP5qDvb3YsO7Qnf3TRiVbGxNG/WYnlM4/o=
-gitlab.com/yawning/edwards25519-extra.git v0.0.0-20211229043746-2f91fcc9fbdb/go.mod h1:gvdJuZuO/tPZyhEV8K3Hmoxv/DWud5L4qEQxfYjEUTo=
 gitlab.com/yawning/obfs4.git v0.0.0-20190120164510-816cff15f425/go.mod h1:uVzlS2REpJUn1Ey9SUKePjW2Qk9yNfNSxYUlbaefaDs=
-gitlab.com/yawning/obfs4.git v0.0.0-20220102012252-cbf3f3cfa09c h1:1aZt0VMNa//m/ci4kOTr0RAKCgVqsl/lDc8yCKAj+pc=
-gitlab.com/yawning/obfs4.git v0.0.0-20220102012252-cbf3f3cfa09c/go.mod h1:M/ySGu25z1AVt2TQ08JY34k1MtMvV253duru0cR+09k=
+gitlab.com/yawning/obfs4.git v0.0.0-20210511220700-e330d1b7024b h1:w/f20IHUkUYEp+xYgpKz4Bs78zms0DbjPZCep5lc0xA=
+gitlab.com/yawning/obfs4.git v0.0.0-20210511220700-e330d1b7024b/go.mod h1:OM1ngEp5brdANPox+rqk2AGTLQvzobyB5Dwm3vu3CgM=
 gitlab.com/yawning/utls.git v0.0.12-1 h1:RL6O0MP2YI0KghuEU/uGN6+8b4183eqNWoYgx7CXD0U=
 gitlab.com/yawning/utls.git v0.0.12-1/go.mod h1:3ONKiSFR9Im/c3t5RKmMJTVdmZN496FNyk3mjrY1dyo=
 gitlab.torproject.org/tpo/anti-censorship/geoip v0.0.0-20210928150955-7ce4b3d98d01/go.mod h1:K3LOI4H8fa6j+7E10ViHeGEQV10304FG4j94ypmKLjY=
@@ -821,7 +817,6 @@ golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897/go.mod h1:LzIPMQfyMNhhGPh
 golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad/go.mod h1:jdWPYTVW3xRLrWPugEBEK3UY2ZEsg3UU495nc5E+M+I=
 golang.org/x/crypto v0.0.0-20210317152858-513c2a44f670/go.mod h1:T9bdIzuCu7OtxOm1hfPfRQxPLYneinmdGuTeoZ9dtd4=
 golang.org/x/crypto v0.0.0-20210513164829-c07d793c2f9a/go.mod h1:P+XmwS30IXTQdn5tA2iutPOUgjI07+tq3H3K9MVA1s8=
-golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/crypto v0.0.0-20210817164053-32db794688a5/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
 golang.org/x/crypto v0.0.0-20211117183948-ae814b36b871/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=