[Attributor][NFCI] Avoid duplication of the InformationCache reference

Summary:
Instead of storing the reference to the InformationCache we now pass it
whenever it might be needed.

Reviewers: sstefan1, uenoku

Subscribers: hiraditya, bollu, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65709

llvm-svn: 367950