Auto merge of #114399 - Zalathar:no-renumber, r=jackh726

coverage: Don't bother renumbering expressions on the Rust side

The LLVM API that we use to encode coverage mappings already has its own code for removing unused coverage expressions and renumbering the rest.

This lets us get rid of our own complex renumbering code, making it easier to change our coverage code in other ways.

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Now that we have tests for coverage mappings (#114843), I've been able to verify that this PR doesn't make the coverage mappings worse, thanks to an explicit simplification step.

Author: bors