Remove backtrace tests, they are broken on newer rust versions #868

Job	Run time
Test features	33s
Test Rust stable on ubuntu	19s
Clippy	13s
Test Rust stable on macOS	20s
Doc tests	26s
Minimal crates versions (stable, ubuntu)	27s
Test Rust stable on windows	19s
Minimal crates versions (stable, macOS)	33s
rustfmt	13s
Test Rust nightly on ubuntu	16s
Minimal crates versions (stable, windows)	1m 9s
Test Rust nightly on macOS	20s
Test Rust nightly on windows	18s
Test Rust 1.65.0 on ubuntu	19s
Test Rust 1.65.0 on macOS	19s
Test Rust 1.65.0 on windows	16s
	6m 20s

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