Revert "Assert that union sizes match"

This reverts commit r67078.
It breaks armv7l-linux-eabihf and sparc-solaris2.11.
http://rubyci.s3.amazonaws.com/scw-9d6766/ruby-trunk/log/20190215T061708Z.diff.html.gz
http://rubyci.s3.amazonaws.com/unstable11s/ruby-trunk/log/20190215T072546Z.diff.html.gz

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67080 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

gc.c

@@ -449,8 +449,6 @@ typedef struct RVALUE {
 #pragma pack(pop)
 #endif
 
-STATIC_ASSERT(rvalue_size, sizeof(((RVALUE*)0)->as) == sizeof(((RVALUE*)0)->as.values));
-
 typedef uintptr_t bits_t;
 enum {
     BITS_SIZE = sizeof(bits_t),