[MLIR][LLVM] Remove disallowlist from LLVM inliner (#75303)

The disallowlist was used as a migration strategy while support was
extended to more side effecting operations. We now (to the best of our
knowledge) support all side effecting operations, so never fail
`isLegalToInline` on any LLVM operation.

There is no test included, because that's exactly the reason for this
change: there are no more unsupported operations in inlining; the
existing tests for unsupported inlines have already been burninated.