[llvm] [NFC][DecoderEmitter] Code cleanup in `DecoderEmitter::emitTable` (PR #158014)

[Sergei Barannikov via llvm-commits]

s-barannikov wrote:

> @s-barannikov any concerns? I know you have some other refactoring with pretty printing in the works

I'll take a closer look by the end of the week if that can wait

https://github.com/llvm/llvm-project/pull/158014