[LinkAllPasses] Remove unused header includes. NFCI

This patch removes some includes from LinkAllPasses.h, that appears
to be unused. Those should have been removed earlier when the
corresponding legacy PM passes were removed.

InstSimplifyPass is a bit special since the legacy PM version of the
pass still exists. But since createInstSimplifyLegacyPass is defined
in Scalar.h and not in InstSimplifyPass.h that particular include
isn't needed anyway.