Remove empty cc_library //aos/logging

It was just pointing to //aos/logging:implementations.  Rename that
cc_library to //aos/logging and delete the empty one.  This is an
attempt to simplify //aos/logging.

Change-Id: Ia182d4695f276da96a5c97c017fc2084187ad5d3
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/aos/BUILD b/aos/BUILD
index 79cd681..34af003 100644
--- a/aos/BUILD
+++ b/aos/BUILD
@@ -179,7 +179,7 @@
         ":realtime",
         ":uuid",
         "//aos:die",
-        "//aos/logging:implementations",
+        "//aos/logging",
     ],
 )