Revert "busybox: fix build for x86 android"

This reverts commit ae51825d, no need for a separate configuration file. Instead, add syscall stubs like those for arm and mips.

Conflicts:
	include-full-x86/autoconf.h
	include-full-x86/usage_compressed.h
	include-minimal-x86/autoconf.h
	include-minimal-x86/usage_compressed.h