aarch64-pe fails of tls-debug tests

These fail to assemble since they use ELF section directives.  There
isn't any need to test for an aarch64 target since that is done in
aarch64.exp.

	* testsuite/gas/aarch64/tls-debug.d: Replace aarch64 target test
	with is_elf_format.
	* testsuite/gas/aarch64/tls-debug-bad.d: Likewise.