i386/AArch64: Remove old xml tests

i386/AArch64: Remove old xml tests

Both the i386, X86_64 and AArch64 builds of gdbserver include a bunch of legacy
xml files, dat files and auto generated C files, when building for unit test.

These tests exists back from when feature target descriptions were added to
prove that the new target descriptions were identical to the original
older versions. The old files are not used for anything other than these tests.

Now that this has been proven, we are not gaining anything by keeping the
original files and tests. Should new functionality be added, it would break
the tests, unless the functionality was backported to the xml. There is no
requirement that we must match the exact xml from N releases ago.  It adds
obfuscation, where as the feature target descriptions were meant to simplify
the code.

In addition, there are a bunch of xml and dat files which are completely unused.

This patch removes the selftests and the target descriptions from gdbserver.

Update the unittest to allow 0 tests (note, this failed on other targets that
never had any tests).

gdb/ChangeLog:

	* aarch64-tdep.c: Remove xml self tests.
	* amd64-linux-tdep.c: Likewise.
	* amd64-tdep.c: Likewise.
	* i386-linux-tdep.c: Likewise.
	* i386-tdep.c: Likewise.

gdb/gdbserver/ChangeLog:

	* configure.srv: Remove legacy xml.
	* linux-aarch64-low.c (initialize_low_arch): Remove
	initialize_low_tdesc call.
	* linux-aarch64-tdesc-selftest.c: Remove file.
	* linux-aarch64-tdesc.h (initialize_low_tdesc): Remove.
	* linux-x86-low.c (initialize_low_arch): Remove
	initialize_low_tdesc call.
	* linux-x86-tdesc-selftest.c: Remove file.
	* linux-x86-tdesc.h (initialize_low_tdesc): Remove.

gdb/testsuite/ChangeLog:

	* gdb.server/unittest.exp: Allow 0 unit tests to run.