GDBserver now is able to generate target descriptions from features, so
don't need to remember these target description files.
Note that it should be i386/amd64-avx-avx512-linux.xml instead of
i386/amd64-avx-avx512.xml in $srv_amd64_linux_xmlfiles. This patch
removes it anyway.
gdb/gdbserver:
2017-09-05 Yao Qi <yao.qi@linaro.org>
* configure.srv (srv_amd64_linux_xmlfiles): Remove
i386/amd64-XXX-linux from it.