[Flang][OpenMP] Remove present modifier application on descriptor (#211856)
This was a minor change upstreamed in the original PR:
https://github.com/llvm/llvm-project/pull/208133
However, it is a modification that needs a little more thought from a
specification perspective before it is rolled out, there's a number of
code bases that depend on the presence modifier being applied only to
the underlying data. However, this leads to inconsistencies when a user
makes use of any reference semantic modifiers when mapping as they
SHOULD be allowed to specify present applying to the descriptor. So, we
need to work out what the correct defualt behaviour is, and regardless
of the default support a user intentionally specifying presence
application on a descriptor via reference semantics.
For now, we will revert to previous state.