[OpenMP][NFC] Simplify targetDataEnd conditions for CopyMember

targetDataEnd and targetDataBegin compute CopyMember/copy differently,
and I don't see why they should.  This patch eliminates one of those
differences by making a simplifying NFC change to targetDataEnd.

The change is NFC as follows.  The change only affects the case when
`!UNIFIED_SHARED_MEMORY || HasCloseModifier`.  In that case, the
following points are always true:

* The value of CopyMember is relevant later only if DelEntry = false.
* DelEntry = false only if one of the following is true:
    * IsLast = false.  In this case, it's always true that CopyMember
      = false = IsLast.
    * `MEMBER_OF && !PTR_AND_OBJ` is true.  In this case, CopyMember =
      IsLast.
* Thus, if CopyMember is relevant, CopyMember = IsLast.

Reviewed By: grokos

Differential Revision: https://reviews.llvm.org/D105990