bitbake: lib: remove unused imports

removed unused imports which made the code harder to read, and slightly
but less efficient

(Bitbake rev: 4367692a932ac135c5aa4f9f2a4e4f0150f76697)

Signed-off-by: Frazer Clews <frazer.clews@codethink.co.uk>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/utils.py

@@ -24,7 +24,6 @@ import fnmatch
 import traceback
 import errno
 import signal
-import ast
 import collections
 import copy
 from subprocess import getstatusoutput