[lit, python] Remove quotes around %python in cache.ll

Summary: We needed quotes around %python before to make python work correctly (on Windows) if the path contains spaces. I recently made a change so that %python now inherently has quotes, so now adding quotes around %python makes the test fail because the quotes cancel each other.

Reviewers: asmith, inglorion

Subscribers: mehdi_amini, eraman, steven_wu, dexonsmith, llvm-commits

Differential Revision: https://reviews.llvm.org/D51244

llvm-svn: 340753