Merge bitcoin/bitcoin#28890: rpc: Remove deprecated -rpcserialversion

fa46cc22bc Remove deprecated -rpcserialversion (MarcoFalke)

Pull request description:

  The flag is problematic for many reasons:

  * It is deprecated
  * It is a global flag, requiring a restart to change, as opposed to a flag that can be set on each RPC invocation
  * It may be hidden in config files by accident, hard to debug, causing LND crashes and bugs, see https://github.com/bitcoin/bitcoin/issues/28730#issuecomment-1780940868
  * It makes performance improvements harder to implement: https://github.com/bitcoin/bitcoin/pull/17529#issuecomment-556082818

  Fix all issues by removing it.

  If there is a use-case, likely a per-RPC flag can be added, if needed.

ACKs for top commit:
  ajtowns:
    crACK fa46cc22bc
  TheCharlatan:
    lgtm ACK fa46cc22bc

Tree-SHA512: 96ba1c60356ce93954fe5c2a59045771c6d1516ad0d9dc436ef1800a1f1b0153f0d5fb78ca99d53ad54ba25fbce36962bdf1d4325aceedfc8154a61347a6a915

src/interfaces/chain.h

@@ -335,9 +335,6 @@ public:
     //! Run function after given number of seconds. Cancel any previous calls with same name.
     virtual void rpcRunLater(const std::string& name, std::function<void()> fn, int64_t seconds) = 0;
 
-    //! Current RPC serialization flags.
-    virtual bool rpcSerializationWithoutWitness() = 0;
-
     //! Get settings value.
     virtual common::SettingsValue getSetting(const std::string& arg) = 0;