rb_cCont: no longer exists

Deleted well over a decade ago in commit 977d66ec99.

include/ruby/internal/globals.h

@@ -47,7 +47,6 @@ RUBY_EXTERN VALUE rb_cObject;
 RUBY_EXTERN VALUE rb_cArray;
 RUBY_EXTERN VALUE rb_cBinding;
 RUBY_EXTERN VALUE rb_cClass;
-RUBY_EXTERN VALUE rb_cCont;
 RUBY_EXTERN VALUE rb_cDir;
 RUBY_EXTERN VALUE rb_cEncoding;
 RUBY_EXTERN VALUE rb_cEnumerator;