Revert "[libunwind] Relax a REQUIRES on a test that passes on FreeBSD"

While it worked for me locally, it appears to be failing on the
FreeBSD 13 buildbot.

This reverts commit ab78962.

Author: arichardson

libunwind/test/forceunwind.pass.cpp

@@ -7,7 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// REQUIRES: linux || freebsd
+// REQUIRES: linux
 
 // TODO: Figure out why this fails with Memory Sanitizer.
 // XFAIL: msan