[clang] [NFC][SemaHLSL] Remove check dependent on non-deterministic root element association (PR #148649)

[Finn Plummer via cfe-commits]

inbelic wrote:

Although, thinking a bit more, we can actually remove this test entirely. The FileCheck portion was just a nicety to check that the SourceLocation was pointing correctly for this case. However, this is redundant with the other checks that exist to do so.

https://github.com/llvm/llvm-project/pull/148649