Revert "Massi's fix for Unity case 358526."

This reverts commit 0ded3104efabfa00308524df573a348e383eb540.
Handle one more case of constraint compatibility.

	* verify.c (mono_generic_param_is_constraint_compatible):
	Handle the case when a variable has a class constraints
	and the target has reference constraint. For example:

	C : string
	T : class

	On the above case, C can satisfy the T constraint.

	Fixes #660685

Conflicts:
	mono/metadata/verify.c