Remove no-op TIME_INIT on deser

Assigning TIME_INIT to nTime was needed to fully re-initialize a dirty
object where the deserialization might skip nTime.
See https://github.com/bitcoin/bitcoin/pull/19020/files#r427620111

Now that the without-nTime logic is removed in commit
dbcb5742c4 and commit
e08770bed1, the logic here can be removed
as well.

Also, remove confusing and redundant preprocessor code.

Also, remove no longer needed version.h include, which was needed for
INIT_PROTO_VERSION.

src/protocol.h

@@ -3,10 +3,6 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#ifndef __cplusplus
-#error This header can only be compiled as C++.
-#endif
-
 #ifndef BITCOIN_PROTOCOL_H
 #define BITCOIN_PROTOCOL_H
 
@@ -15,10 +11,9 @@
 #include <serialize.h>
 #include <streams.h>
 #include <uint256.h>
-#include <version.h>
 
+#include <cstdint>
 #include <limits>
-#include <stdint.h>
 #include <string>
 
 /** Message header.
@@ -420,7 +415,6 @@ public:
             use_v2 = s.GetVersion() & ADDRV2_FORMAT;
         }
 
-        SER_READ(obj, obj.nTime = TIME_INIT);
         READWRITE(obj.nTime);
         // nServices is serialized as CompactSize in V2; as uint64_t in V1.
         if (use_v2) {