Delete "$message_type" special case from with_json_contains_unordered #13017
Description
#13016 added the following hack to accommodate rust-lang/rust#115691, because for now, some compilers supported by Cargo emit "$message_type" in their diagnostics and some do not.
cargo/crates/cargo-test-support/src/compare.rs
Lines 597 to 607 in 71cd3a9
As soon as Cargo's MSRV increases past 1.76, this should be deleted.
According to @epage, the JSON testing infrastructure is intended to be independent of rustc in the long term. Compiler-specific special cases run counter to this effort to switch to a generic third-party library.
Of course deleting the special case only defers the issue until some other JSON change happens in a future release. We still need to figure out how the generic tool should accommodate this in a principled way.