[GDBserver] Shorten srv_i386_linux_xmlfiles

GDBserver now is able to generate target descriptions from features, so
don't need to remember these target description files.

gdb/gdbserver:

2017-09-05  Yao Qi  <yao.qi@linaro.org>

	* configure.srv (srv_i386_linux_xmlfiles): Remove
	i386/i386-XXX-linux.xml from it.