rpc: fix broken RPCExamples for waitforblock(height)

Summary:
Fixes the following RPCExamples:
-> ExampleCli waitforblock (removed comma between arguments)
-> ExampleCli waitforblockheight (removed comma between arguments)
-> ExampleRpc waitforblockheight (removed quotation marks around integer argument)

This is a backport of Core PR18398

Test Plan:

ninja && src/bitcoind &
sleep 5
src/bitcoin-cli waitforblockheight 100 1000
src/bitcoin-cli waitforblock  "0000000000079f8ef3d2c688c244eb7a4570b24c9ed7b4a8c619eb02596f8862" 1000

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8884