BUILD: delete-project: Remove redundant Mockito dependency

Mockito is already reachable transitively from
plugins/delete-project:delete-project_tests, e.g.:

  bazel query 'somepath(plugins/delete-project:delete-project_tests,
                        //lib/mockito)'

Remove the explicit dependency to avoid duplication and keep the
BUILD file minimal.

Change-Id: I7a305da2e3feaa9537f15127433bd86068e79b0f

BUILD

diff --git a/BUILD b/BUILD
index 1bfb09a..3caf093 100644
--- a/BUILD
+++ b/BUILD
@@ -35,6 +35,5 @@
     visibility = ["//visibility:public"],
     exports = PLUGIN_DEPS + PLUGIN_TEST_DEPS + [
         ":delete-project__plugin",
-        "@mockito//jar",
     ],
 )