[InstSimplify] Report "Changed" also when only deleting dead instructions

Summary:
Make sure that we report that changes has been made
by InstSimplify also in situations when only trivially
dead instructions has been removed. If for example a call
is removed the call graph must be updated.

Bug seem to have been introduced by llvm-svn r367173
(commit 02b9e45a), since the code in question
was rewritten in that commit.

Reviewers: spatel, chandlerc, foad

Reviewed By: spatel

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65973

llvm-svn: 368401