[llvm] Revert "[MC] Explicitly mark MCSymbol for MO_ExternalSymbol" (PR #133291)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

> @efriedma-quic can you please tell us how to add test for such functionality ?

If you want to check asm output, just run `llc`.  If you want to check the contents of an object file, you can do something like `llc -filetype=obj | llvm-objdump --syms -`.

https://github.com/llvm/llvm-project/pull/133291