[gas][testsuite] Don't specify arch in testsuite output

[gas][testsuite] Don't specify arch in testsuite output

My testcase matched against a file format of elf64-littleaarch64 in the
objdump output.  This was unnecessarily restrictive and causes testcase
failures on aarch64_be.

Here we remove that restriction.
Committed as obvious.

Testing done on aarch64_be-none-elf gas to see the failure goes away.

gas/ChangeLog:

2019-05-09  Matthew Malcomson  <matthew.malcomson@arm.com>

	* testsuite/gas/aarch64/sve2.d: Remove file format restriction.