[OpenMP][NFC] Eliminate CopyMember from targetDataEnd

This patch is based on comments in D105990.  It is NFC according to
the following observations:

1. `CopyMember` is computed as `!IsHostPtr && IsLast`.
2. `DelEntry` is true only if `IsLast` is true.

We apply those observations in order:

```
if ((DelEntry || Always || CopyMember) && !IsHostPtr)

if ((DelEntry || Always || IsLast) && !IsHostPtr)

if ((Always || IsLast) && !IsHostPtr)
```

Reviewed By: grokos

Differential Revision: https://reviews.llvm.org/D107926