[clang] [Clang] [CodeGen] Remove special handling for constant `switch` conditions (PR #233595)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

See 0725a8b653ea4a7dedddfae6e65256dac8210dfd / 0709542628f3e11d07eb4a57e62e1818b07fb808.  I wouldn't be surprised if this blows up a Linux kernel build somehow.  If it doesn't, fine, I guess.

There's probably some less cumbersome way to do an equivalent optimization leveraging the walk we do in VarBypassDetector.

https://github.com/llvm/llvm-project/pull/233595