[llvm] [openmp] [Offload] Remove standalone build in favor of 'runtimes' (PR #162904)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> Seems like pretty mechanical. LGTM.

Thanks, I'll let this sit for a bit until I get an OK from Ethan since he's working on removing the one user of this i know of.

https://github.com/llvm/llvm-project/pull/162904