[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:
    
    2017-07-07  Yao Qi  <yao.qi@linaro.org>
    
    	* configure.srv (srv_i386_linux_xmlfiles): Remove
    	i386/i386-XXX-linux.xml from it.