[OpenMP][NFC] Remove hard-coded line numbers from test

Otherwise, it's painful to insert new code.  There are many existing
examples in the same test file where the line numbers are not
hard-coded.

I intend to do the same for several other OpenMP tests, but I want to
be sure there are no objections before I spend time on it.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D82224