Clean up neo.lib.protocol

When using network byte order ('!'), the size of struct items is independant of
the platform. They have never changed from one version of Python to another.

neo/lib/protocol.py

@@ -14,7 +14,6 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-import socket
 import sys
 import traceback
 from cStringIO import StringIO
@@ -26,12 +25,6 @@ PROTOCOL_VERSION = 12
 MIN_PACKET_SIZE = 10
 MAX_PACKET_SIZE = 0x4000000
 PACKET_HEADER_FORMAT = Struct('!LHL')
-# Check that header size is the expected value.
-# If it is not, it means that struct module result is incompatible with
-# "reference" platform (python 2.4 on x86-64).
-assert PACKET_HEADER_FORMAT.size == 10, \
-    'Unsupported platform, packet header length = %i' % \
-    (PACKET_HEADER_FORMAT.size, )
 RESPONSE_MASK = 0x8000
 
 class Enum(tuple):
@@ -161,16 +154,12 @@ cell_state_prefix_dict = {
 }
 
 # Other constants.
-INVALID_UUID = 0
-INVALID_TID = '\xff' * 8
+INVALID_TID = \
 INVALID_OID = '\xff' * 8
 INVALID_PARTITION = 0xffffffff
-INVALID_ADDRESS_TYPE = socket.AF_UNSPEC
 ZERO_HASH = '\0' * 20
-ZERO_TID = '\0' * 8
+ZERO_TID = \
 ZERO_OID = '\0' * 8
-OID_LEN = len(INVALID_OID)
-TID_LEN = len(INVALID_TID)
 MAX_TID = '\x7f' + '\xff' * 7 # SQLite does not accept numbers above 2^63-1
 
 # High-order byte: