Revert reserved immediate word shifts with imm[5]!=0 #661

Job	Run time
rvgo-lint	24s
rvgo-abigen	50s
op-program-test	2m 12s
check-optimism-version-match	29s
rvgo-tests	11m 51s
rvsol-lint	8s
rvsol-tests	1m 5s
	16m 59s

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