[OpenMP] Remove implicit data sharing code gen that aims to use device shared memory

Summary: Remove this scheme for now since it will be covered by another more generic scheme using global memory. This code will be worked into an optimization for the generic data sharing scheme. Removing this completely and then adding it via future patches will make all future data sharing patches cleaner.

Reviewers: ABataev, carlo.bertolli, caomhin

Reviewed By: ABataev

Subscribers: jholewinski, guansong, cfe-commits

Differential Revision: https://reviews.llvm.org/D43625

llvm-svn: 326948