devel/libpthread-stubs: remove port

libpthread-stubs >= 0.4 isn't granular: checks too few or often unused
pthread symbols. On FreeBSD it always added -pthread even if pthread
stubs libc would be enough. Consumers usually avoid libpthread-stubs
dependency on Linux, duplicating the logic. So, remove the wrapper.

PR:		269453
See also:	https://gitlab.freedesktop.org/xorg/lib/pthread-stubs/-/issues/2
Inspired by:	Arch, Fedora, OpenBSD, PkgSrc, Void
Approved by:	ashish (maintainer)

MOVED

@@ -17786,3 +17786,4 @@ databases/postgresql10-plpython||2023-03-07|Has expired: PostgreSQL 10 has reach
 databases/postgresql10-pltcl||2023-03-07|Has expired: PostgreSQL 10 has reached end-of-life
 databases/postgresql10-server||2023-03-07|Has expired: PostgreSQL 10 has reached end-of-life
 audio/ximp3||2023-03-09|Has expired: Abandonware and obsolete, uses old decoder library and no ID3v2 support
+devel/libpthread-stubs||2023-03-12|No consumers left and never supported pthread stubs in libc on FreeBSD

devel/Makefile

@@ -1341,7 +1341,6 @@
     SUBDIR += libpo6
     SUBDIR += libpololu-avr
     SUBDIR += libpru
-    SUBDIR += libpthread-stubs
     SUBDIR += libqb
     SUBDIR += libqcow
     SUBDIR += libqsbr