testsuite: Rename scanltranstree.exp -> scanltrans.exp

Since r15-3254-g3f51f0dc88ec21c1ec79df694200f10ef85915f4
added scan-ltrans-rtl* variants to scanltranstree.exp, it no longer
makes sense to have "tree" in the name.  This renames the file
accordingly and updates users.

libatomic/ChangeLog:

	* testsuite/lib/libatomic.exp: Load scanltrans.exp instead of
	scanltranstree.exp.

libgomp/ChangeLog:

	* testsuite/lib/libgomp.exp: Load scanltrans.exp instead of
	scanltranstree.exp.

libitm/ChangeLog:

	* testsuite/lib/libitm.exp: Load scanltrans.exp instead of
	scanltranstree.exp.

libphobos/ChangeLog:

	* testsuite/lib/libphobos-dg.exp: Load scanltrans.exp instead of
	scanltranstree.exp.

libvtv/ChangeLog:

	* testsuite/lib/libvtv.exp: Load scanltrans.exp instead of
	scanltranstree.exp.

gcc/testsuite/ChangeLog:

	* gcc.dg-selftests/dg-final.exp: Load scanltrans.exp instead of
	scanltranstree.exp.
	* lib/gcc-dg.exp: Likewise.
	* lib/scanltranstree.exp: Rename to ...
	* lib/scanltrans.exp: ... this.