[NFC] Remove extra headers included in Loop Unroll and LoopUnrollAndJam files

Summary:
This refactor patch removes some header files which are not needed and also add some to meet IWYU principles.

Reviewers: rnk (Reid Kleckner), Meinersbur (Michael Kruse), dmgreen (Dave Green)

Reviewed By: dmgreen (Dave Green), rnk (Reid Kleckner), Meinersbur (Michael Kruse)

Subscribers: dmgreen (Dave Green), Whitney (Whitney Tsang), hiraditya (Aditya Kumar), zzheng (Z. Zheng), llvm-commits, LLVM

Tag: LLVM

Differential Revision: https://reviews.llvm.org/D73498