rpc: use rtlil instead of ilang #3600

Job	Run time
check-links	45s
document	45s
smoke (amaranth-lang/amaranth-boards)	34s
smoke (amaranth-lang/amaranth-stdio)	58s
test (3.9)	2m 6s
smoke (amaranth-lang/amaranth-soc)	59s
test (3.10)	2m 27s
test (3.11)	2m 46s
test (3.12)	3m 4s
test (3.13)	2m 45s
test (pypy-3.9)	6m 11s
test (pypy-3.10)	5m 7s
test (3.14-dev)	1m 34s
publish-docs	8s
publish-docs-dev	0s
required	1s
publish-package	17s
publish-schemas	5s
publish-release	0s
	30m 32s

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