[llvm] RuntimeLibcalls: Remove darwin override of half convert libcalls (PR #148782)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Aug 4, 12:43 AM UTC**: [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/148782) rebased this pull request as part of a merge.


https://github.com/llvm/llvm-project/pull/148782