Revert "[OPENMP] Fixed codegen for 'omp cancel' construct."

Summary:
r286944 introduced bugs detected by ASAN as use-after-return.
r287025 have not fixed them completely.

This reverts commit r286944 and r287025.

Reviewers: ABataev

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D26720

llvm-svn: 287069