[clang] Revert "[Clang] Fix missed initializer instantiation bug for variable templates" (PR #140930)

[Paul Kirth via cfe-commits]

ilovepi wrote:

Well, its not the easiest case to reduce, since there's lots of ways the two errors in question could happen. That code has been accepted by both GCC and clang for some time though, so at the very least we need guidance on what is wrong with it.

>From what I've been able to tell, instantiation now happens earlier and deduction fails, despite there being a valid deduction guide. @frobtech is more familar w/ this code though and can provide more insight.

https://github.com/llvm/llvm-project/pull/140930