test: drop unused testnet3 magic bytes

Author: Sjors

test/functional/test_framework/messages.py

@@ -78,11 +78,10 @@
 DEFAULT_MEMPOOL_EXPIRY_HOURS = 336  # hours
 
 MAGIC_BYTES = {
-    "mainnet": b"\xf9\xbe\xb4\xd9",   # mainnet
-    "testnet3": b"\x0b\x11\x09\x07",  # testnet3
-    "testnet4": b"\x1c\x16\x3f\x28",  # testnet4
-    "regtest": b"\xfa\xbf\xb5\xda",   # regtest
-    "signet": b"\x0a\x03\xcf\x40",    # signet
+    "mainnet": b"\xf9\xbe\xb4\xd9",
+    "testnet4": b"\x1c\x16\x3f\x28",
+    "regtest": b"\xfa\xbf\xb5\xda",
+    "signet": b"\x0a\x03\xcf\x40",
 }
 
 def sha256(s):