Remove p2pEnabled from Chain interface (Antoine Riard)
Pull request description:
RPC server starts in warmup mode, it can't process yet calls, then follows connection manager initialization and finally RPC server get out of warmup mode. RPC calls shouldn't be able to get P2P disabled errors because once we initialize g_connman it's not unset until shutdown, after RPC server has been stopped.
@mzumsande comment in #15713 let me thought that `p2pEnabled` was maybe useless, `g_connman` is always initialized before RPC server is getting out of warmup. These checks against P2P state were introduced in https://github.com/bitcoin/bitcoin/pull/8085/commits/5b446dd5b11d4f403554bc2dd5a7a94c7d20422a.
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Backport of Core PR16503