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/testing/BUILD b/aos/testing/BUILD
index ede1160..787fdda 100644
--- a/aos/testing/BUILD
+++ b/aos/testing/BUILD
@@ -27,7 +27,7 @@
     visibility = ["//visibility:public"],
     deps = [
         ":googletest",
-        "//aos/logging:implementations",
+        "//aos/logging",
         "//aos/stl_mutex",
         "@com_google_absl//absl/base",
     ],