refactor: Rename CTransaction::nVersion to version

In order to ensure that the change of nVersion to a uint32_t in the
previous commit has no effect, rename nVersion to version in this commit
so that reviewers can easily spot if a spot was missed or if there is a
check somewhere whose semantics have changed.

test/functional/rpc_rawtransaction.py

@@ -465,28 +465,28 @@ class RawTransactionsTest(BitcoinTestFramework):
         # Test the minimum transaction version number that fits in a signed 32-bit integer.
         # As transaction version is serialized unsigned, this should convert to its unsigned equivalent.
         tx = CTransaction()
-        tx.nVersion = 0x80000000
+        tx.version = 0x80000000
         rawtx = tx.serialize().hex()
         decrawtx = self.nodes[0].decoderawtransaction(rawtx)
         assert_equal(decrawtx['version'], 0x80000000)
 
         # Test the maximum transaction version number that fits in a signed 32-bit integer.
         tx = CTransaction()
-        tx.nVersion = 0x7fffffff
+        tx.version = 0x7fffffff
         rawtx = tx.serialize().hex()
         decrawtx = self.nodes[0].decoderawtransaction(rawtx)
         assert_equal(decrawtx['version'], 0x7fffffff)
 
         # Test the minimum transaction version number that fits in an unsigned 32-bit integer.
         tx = CTransaction()
-        tx.nVersion = 0
+        tx.version = 0
         rawtx = tx.serialize().hex()
         decrawtx = self.nodes[0].decoderawtransaction(rawtx)
         assert_equal(decrawtx['version'], 0)
 
         # Test the maximum transaction version number that fits in an unsigned 32-bit integer.
         tx = CTransaction()
-        tx.nVersion = 0xffffffff
+        tx.version = 0xffffffff
         rawtx = tx.serialize().hex()
         decrawtx = self.nodes[0].decoderawtransaction(rawtx)
         assert_equal(decrawtx['version'], 0xffffffff)