Merge #19293: net: Avoid redundant and confusing FAILED log

fa1904e net: Remove dead logging code (MarcoFalke)
fac12eb net: Avoid redundant and confusing FAILED log (MarcoFalke)

Pull request description:

  Remove a redundant and confusing "FAILED" log message and gets rid of the unused return type in `ProcessMessage`

ACKs for top commit:
  jnewbery:
    utACK fa1904e
  gzhao408:
    utACK bitcoin/bitcoin@fa1904e
  troygiorshev:
    ACK fa1904e
  naumenkogs:
    utACK fa1904e

Tree-SHA512: bfa553d5efa022727ed17877fb7c08c14849d804fe6d6a7ce172d513857beba35de41ea40b27ff1aedf68b81e2cda7b2a948ac985fcaaf1b6cfb96cce4837c90

Author: fanquake