`wasmi_ir`: remove `InstrSequence` type #4515

Job	Run time
Coverage	3m 52s
Audit	15s
Build	1m 30s
Clippy	55s
Documentation	31s
Formatting	12s
Fuzz (translate)	3m 29s
Check mininum supported Rust version	18s
Fuzz (execute)	3m 29s
Miri	7m 0s
Miri (spec)	6m 20s
Fuzz (differential)	3m 42s
Test (Address Sanitizer)	2m 40s
uDeps	50s
Test (ubuntu-latest)	1m 28s
Test (windows-latest)	2m 31s
Test (macos-latest)	1m 18s
	40m 20s

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