Revert "SLPVectorizer: Ignore users that are insertelements we can reschedule them"

This reverts commit r205018.

Conflicts:
	lib/Transforms/Vectorize/SLPVectorizer.cpp
	test/Transforms/SLPVectorizer/X86/insert-element-build-vector.ll

This is breaking libclc build.

llvm-svn: 205260