MIPS/GAS/testsuite: Drop the `mips16e-' prefix from SAVE/RESTORE tests

In preparation to running these tests against regular MIPS instructions.

	gas/
	* testsuite/gas/mips/mips16e-save.d: Rename to...
	* testsuite/gas/mips/save.d: ... this.
	* testsuite/gas/mips/mips16e-save-err.d: Update the
	`error-output' option and rename to...
	* testsuite/gas/mips/save-err.d: ... this.
	* testsuite/gas/mips/mips16e-save-err.l: Rename to...
	* testsuite/gas/mips/save-err.l: ... this.
	* testsuite/gas/mips/mips16e-save.s: Rename to...
	* testsuite/gas/mips/save.s: ... this.
	* testsuite/gas/mips/mips16e-save-err.s: Rename to...
	* testsuite/gas/mips/save-err.s: ... this.
	* testsuite/gas/mips/mips.exp: Rename `mips16e-save' and
	`mips16e-save-err' invocations to `save' and `save-err'
	respectively and reorder these tests away from MIPS16 tests.