deps: remove unused feature `subxt/substrate-compat` #13686

Job	Run time
isdraft / isdraft	1s
preflight / preflight	46s
preflight / ci-versions	1m 6s
check-revive-stable-uapi-polkavm	2m 33s
build-runtimes-polkavm	8m 34s
build-subkey	4m 16s
All build misc jobs passed	1s
	17m 17s

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