Remove unused imports

There are several imports that are not used.  Remove them.

Change-Id: I2ac3be66827bd68d3faedcef7d6bbf30ea01d3f2
diff --git a/subcmds/cherry_pick.py b/subcmds/cherry_pick.py
index 8da3a75..7890af4 100644
--- a/subcmds/cherry_pick.py
+++ b/subcmds/cherry_pick.py
@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import sys, re, string, random, os
+import sys, re
 from command import Command
 from git_command import GitCommand