Remove configure check prohibiting threaded libpython on OpenBSD.

According to recent tests, this case now works fine, so there's no reason
to reject it anymore.  (Even if there are still some OpenBSD platforms
in the wild where it doesn't work, removing the check won't break any case
that worked before.)

We can actually remove the entire test that discovers whether libpython
is threaded, since without the OpenBSD case there's no need to know that
at all.

Per report from Davin Potts.  Back-patch to all active branches.

config/python.m4

@@ -97,18 +97,4 @@ AC_SUBST(python_libdir)[]dnl
 AC_SUBST(python_libspec)[]dnl
 AC_SUBST(python_additional_libs)[]dnl
 
-# threaded python is not supported on OpenBSD
-AC_MSG_CHECKING(whether Python is compiled with thread support)
-pythreads=`${PYTHON} -c "import sys; print(int('thread' in sys.builtin_module_names))"`
-if test "$pythreads" = "1"; then
-  AC_MSG_RESULT(yes)
-  case $host_os in
-  openbsd*)
-    AC_MSG_ERROR([threaded Python not supported on this platform])
-    ;;
-  esac
-else
-  AC_MSG_RESULT(no)
-fi
-
 ])# PGAC_CHECK_PYTHON_EMBED_SETUP

configure

@@ -7526,23 +7526,6 @@ python_additional_libs=`${PYTHON} -c "import distutils.sysconfig; print(' '.join
 $as_echo "${python_libspec} ${python_additional_libs}" >&6; }
 
 
-# threaded python is not supported on OpenBSD
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether Python is compiled with thread support" >&5
-$as_echo_n "checking whether Python is compiled with thread support... " >&6; }
-pythreads=`${PYTHON} -c "import sys; print(int('thread' in sys.builtin_module_names))"`
-if test "$pythreads" = "1"; then
-  { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
-$as_echo "yes" >&6; }
-  case $host_os in
-  openbsd*)
-    as_fn_error $? "threaded Python not supported on this platform" "$LINENO" 5
-    ;;
-  esac
-else
-  { $as_echo "$as_me:${as_lineno-$LINENO}: result: no" >&5
-$as_echo "no" >&6; }
-fi
-
 
 
   # We need libpython as a shared library.  With Python >=2.5, we