[NFC] Re-enable* MSVC C4503 diagnostic (#182049)
From MSDN:
https://learn.microsoft.com/en-us/cpp/error-messages/compiler-warnings/compiler-warning-level-1-c4503?view=msvc-170
> This compiler warning is obsolete and is not generated in Visual
> Studio 2017 and later compilers.
We require at least MSVC 2019 at this point, so no need to keep
suppressing this diagnostic. So this "re-enables" it, even though it
provides no value.
