transaction: remove unused mmap-related code

lib/transaction.py

@@ -32,7 +32,6 @@ import struct
 #
 import struct
 import StringIO
-import mmap
 import random
 
 NO_SIGNATURE = 'ff'
@@ -55,16 +54,6 @@ class BCDataStream(object):
         else:
             self.input += bytes
 
-    def map_file(self, file, start):  # Initialize with bytes from file
-        self.input = mmap.mmap(file.fileno(), 0, access=mmap.ACCESS_READ)
-        self.read_cursor = start
-
-    def seek_file(self, position):
-        self.read_cursor = position
-
-    def close_file(self):
-        self.input.close()
-
     def read_string(self):
         # Strings are encoded depending on length:
         # 0 to 252 :  1-byte-length followed by bytes (if any)