Remove lzma support and add notes about squashfs tools #2620

Job	Run time
Check (stable)	1m 59s
Check (1.65.0)	2m 23s
Cross (aarch64-linux-android)	5m 41s
Cross (aarch64-unknown-linux-gnu)	4m 14s
Cross (aarch64-unknown-linux-musl)	4m 33s
Deny (advisories)	35s
Deny (bans licenses sources)	25s
Clippy	1m 42s
Documentation	1m 32s
Format	11s
Hack	2m 50s
Lint markdown files	46s
Tests	7m 6s
Tools	4m 23s
	38m 20s

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