docs: Remove `lightning-` prefix from all RPCs #11903

Job	Run time
Check Nix Flake	16m 45s
Pre-build checks	1m 11s
Run fuzz regression tests	0s
Compile CLN ${{ matrix.cfg }}	0s
Valgrind Test CLN ${{ matrix.name }}	0s
Test CLN ${{ matrix.name }}	0s
Run unit tests	0s
Sanitizers Test CLN	0s
Test minimum supported BTC v${{ matrix.MIN_BTC_VERSION }} with ${{ matrix.NAME }}	0s
CI completion	0s
	17m 56s

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