Remove redundant calls to isMaterializable.

This removes calls to isMaterializable in the following cases:

* It was redundant with a call to isDeclaration now that isDeclaration returns
  the correct answer for materializable functions.
* It was followed by a call to Materialize. Just call Materialize and check EC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221050 91177308-0d34-0410-b5e6-96231b3b80d8