Remove alias.gitiles as it points to non-existing BUCK target

The Ib8f1870390cbfd29ef0c5a062c15e060ce6116bd removed the 'gitiles' target
from the /BUCK but didn't remove the alias pointing to it.

Change-Id: Idbd247d6d141a52ea08d74a1895fee3378a07dae

.buckconfig

diff --git a/.buckconfig b/.buckconfig
index 01c79be..adac013 100644
--- a/.buckconfig
+++ b/.buckconfig
@@ -1,5 +1,4 @@
 [alias]
-  gitiles = //:gitiles
   all = //:all
   in = //:install
   mvn_install = //:install