Remove dominator check in fold_using_range::range_of_phi.

Remove dominator check in fold_using_range::range_of_phi.

Revert the following patch, as it was an artifact of diagnostic code
being run with improper IL.

commit 64b80b8819f9ea74712625bceb0ec4388e25f67d
Author: Aldy Hernandez <aldyh@redhat.com>
Date:   Tue Sep 21 08:28:28 2021 +0200

    Do not query SCEV in range_of_phi unless dominators are available.

    SCEV won't work without dominators and we can get called without
    dominators from debug_ranger.

gcc/ChangeLog:

	* gimple-range-fold.cc (fold_using_range::range_of_phi):
	Remove dominator check.