Remove versioning mention for TWEAK

IMO it doesn't really belong in a main text, especially mentions of specific compilers.

If anything, this type of stuff should be in a separate document, similar to what perldoc perldelta does.

doc/Language/objects.pod6

@@ -444,7 +444,7 @@ example above).
 
 After the C<BUILD> methods have been called, methods named C<TWEAK> are
 called, if they exist, again with all the named arguments that were passed
-to C<new>. (C<TWEAK> is a new feature in v6.d / Rakudo 2016.11)
+to C<new>.
 
 Due to the nature of the default behavior of C<BUILDALL> and custom C<BUILD>
 submethods, named arguments to the constructor C<new> derived from C<Mu> can