tracing: simplify level event macros #6063

Job	Run time
cargo check	5m 33s
cargo fmt	-1s
cargo test (${{ matrix.rust }} on ${{ matrix.os }})	-1s
warnings	-1s
cargo check (+MSRV -Zminimal-versions)	-1s
cargo test (wasm)	-1s
build tests (wasm)	-1s
cargo test (feature-specific)	-1s
cargo check (tracing macros)	-1s
cargo check (feature combinations)	-1s
all systems go!	0s
	5m 24s

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