[OpenMP] Fix performance regression in SPEC kdtree test

Make __ompt_implicit_task_end a static function and remove the inline part.  Remove
pId variable that is unused.  This fixes small regression in SPEC kdtree benchmark.
Also reformat some of __ompt_implicit_task_end.

Differential Revision: https://reviews.llvm.org/D55788


git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@351221 91177308-0d34-0410-b5e6-96231b3b80d8