rpc: use rtlil instead of ilang #3601

Job	Run time
check-links	1m 45s
test (3.9)	2m 22s
document	48s
smoke (amaranth-lang/amaranth-boards)	33s
test (3.10)	2m 21s
smoke (amaranth-lang/amaranth-stdio)	55s
test (3.11)	2m 56s
smoke (amaranth-lang/amaranth-soc)	57s
test (3.12)	3m 30s
test (3.13)	3m 4s
test (pypy-3.9)	6m 34s
test (pypy-3.10)	4m 50s
test (3.14-dev)	1m 33s
publish-docs	13s
publish-docs-dev	0s
required	1s
publish-package	31s
publish-schemas	17s
publish-release	0s
	33m 10s

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