[clang] [Analyzer][NFC] Remove redundant function call (PR #75076)

[Gábor Spaits via cfe-commits]

spaits wrote:

It is a great idea to use assertions here. It is exactly the context in which they should be used. I will add that. Thank you for the review.

I have also thought about a possible different caller but I think it is very unlikely. These `ExpressionHandler`s are basically visitor like classes for this tracking mechanism, if I am correct. Their purpose is to track other values or append `BugReporterVisitor`s to the `PathSensitiveBugReport`.

https://github.com/llvm/llvm-project/pull/75076