Remove features/i386/i386-*linux.c

Now, features/i386/i386-XXX-linux.c are not used, remove them.

gdb:

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

	* features/Makefile (XMLTOC): Remove i386/i386-XX-linux.xml.
	* features/i386/i386-avx-avx512-linux.c: Remove.
	* features/i386/i386-avx-linux.c: Remove.
	* features/i386/i386-avx-mpx-avx512-pku-linux.c: Remove.
	* features/i386/i386-avx-mpx-linux.c: Remove.
	* features/i386/i386-linux.c: Remove.
	* features/i386/i386-mmx-linux.c: Remove.
	* features/i386/i386-mpx-linux.c: Remove.