doc: Document that the OBJ creation functions are now thread safe.

With the OBJ_ thread locking in place, these documentation changes are not
required.

This reverts commit 0218bcd.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #15713)

(cherry picked from commit 06394a6)
Reviewed-by: Hugo Landau <hlandau@openssl.org>

doc/man3/OBJ_nid2obj.pod

@@ -142,6 +142,8 @@ These functions cannot return B<const> because an B<ASN1_OBJECT> can
 represent both an internal, constant, OID and a dynamically-created one.
 The latter cannot be constant because it needs to be freed after use.
 
+These functions were not thread safe in OpenSSL 3.0 and before.
+
 =head1 RETURN VALUES
 
 OBJ_nid2obj() returns an B<ASN1_OBJECT> structure or B<NULL> is an
@@ -180,12 +182,6 @@ Create a new object directly:
 
  obj = OBJ_txt2obj("1.2.3.4", 1);
 
-=head1 BUGS
-
-Neither OBJ_create() nor OBJ_add_sigid() do any locking and are thus not
-thread safe.  Moreover, none of the other functions should be called while
-concurrent calls to these two functions are possible.
-
 =head1 SEE ALSO
 
 L<ERR_get_error(3)>

doc/man7/provider-base.pod

@@ -265,7 +265,6 @@ It will treat as success the case where the OID already exists (even if the
 short name I<sn> or long name I<ln> provided as arguments differ from those
 associated with the existing OID, in which case the new names are not
 associated).
-This function is not thread safe.
 
 The core_obj_add_sigid() function registers a new composite signature algorithm
 (I<sign_name>) consisting of an underlying signature algorithm (I<pkey_name>)
@@ -280,7 +279,6 @@ signature algorithm already exists (even if registered against a different
 underlying signature or digest algorithm). For I<digest_name>, NULL or an
 empty string is permissible for signature algorithms that do not need a digest
 to operate correctly. The function returns 1 on success or 0 on failure.
-This function is not thread safe.
 
 CRYPTO_malloc(), CRYPTO_zalloc(), CRYPTO_free(), CRYPTO_clear_free(),
 CRYPTO_realloc(), CRYPTO_clear_realloc(), CRYPTO_secure_malloc(),
@@ -609,6 +607,11 @@ or maximum. A -1 indicates that the group should not be used in that protocol.
 
 =back
 
+=head1 NOTES
+
+The core_obj_create() and core_obj_add_sigid() functions were not thread safe
+in OpenSSL 3.0.
+
 =head1 EXAMPLES
 
 This is an example of a simple provider made available as a