scripted-diff: Rename ValidAsCString to ContainsNoNUL

-BEGIN VERIFY SCRIPT-
 sed -i 's,ValidAsCString,ContainsNoNUL,g' $(git grep -l ValidAsCString)
-END VERIFY SCRIPT-

src/netaddress.cpp

@@ -210,7 +210,7 @@ static void Checksum(Span<const uint8_t> addr_pubkey, uint8_t (&checksum)[CHECKS
 
 bool CNetAddr::SetSpecial(const std::string& addr)
 {
-    if (!ValidAsCString(addr)) {
+    if (!ContainsNoNUL(addr)) {
         return false;
     }