message: doc: remove mention of system univalue
  Should have been part of
diff: @@ -46,7 +46,6 @@ Optional dependencies:
  libdb4.8 | Berkeley DB | Optional, wallet storage (only needed when legacy wallet enabled)
  qt | GUI | GUI toolkit (only needed when GUI enabled)
  libqrencode | QR codes in GUI | Optional for generating QR codes (only needed when GUI enabled)
  - univalue | Utility | JSON parsing and encoding (bundled version will be used unless --with-system-univalue passed to configure)
  libzmq3 | ZMQ notification | Optional, allows generating ZMQ notifications (requires ZMQ version >= 4.0.0)
  sqlite3 | SQLite DB | Optional, wallet storage (only needed when descriptor wallet enabled)
  systemtap | Tracing (USDT) | Optional, statically defined tracepoints
  