Android.bp: remove subdirs

They're deprecated and not needed as Soong automatically recurses.
diff --git a/Android.bp b/Android.bp
index 03c85c1..64cdc29 100644
--- a/Android.bp
+++ b/Android.bp
@@ -13,10 +13,3 @@
 // limitations under the License.
 
 soong_namespace {}
-
-subdirs = [
-    "qcom/pd-mapper",
-    "qcom/qrtr",
-    "qcom/rmtfs",
-    "qcom/tqftpserv",
-]