remove needless double type conversion

i got confused and thought i was setting the environment (in which case you need to cast to str anyways, so this was wrong even then)

borg/helpers.py

@@ -13,7 +13,7 @@ try:
 except ImportError:
     def get_terminal_size(fallback=(80, 24)):
         TerminalSize = namedtuple('TerminalSize', ['columns', 'lines'])
-        return TerminalSize(int(os.environ.get('COLUMNS', int(fallback[0]))), int(os.environ.get('LINES', int(fallback[1]))))
+        return TerminalSize(int(os.environ.get('COLUMNS', fallback[0])), int(os.environ.get('LINES', fallback[1])))
 import sys
 import time
 import unicodedata