[clang-tools-extra] [lld] [llvm] tools: Remove unused PluginLoader includes (PR #117644)

[Matt Arsenault via cfe-commits]

arsenm wrote:

Apparently the header adds a static define of the option into the included header. This means that it's untested/unused in the llc, lld, lli, llvm-lto, and opt cases. It does appear to have some tests for bug point and clang tidy 

https://github.com/llvm/llvm-project/pull/117644