Use all *.aconfig source in flags BP instead of maintaining a list

Adding sources one by one isn't necessary, and causes merge conflicts
each time a new one is added (assuming you've added one too).

We can help everyone skip that step and use all sources in the flags
folder automatically.

Tag: #refactor
Bug: 317394189
Flag: EXEMPT build file change only
Test: m com.android.btservices
Change-Id: I506b1f9453a6cab7db2bcd7263ad331829c0d2a1

flags/Android.bp

@@ -7,18 +7,7 @@ aconfig_declarations {
     name: "bluetooth_aconfig_flags",
     package: "com.android.bluetooth.flags",
     srcs: [
-        "a2dp.aconfig",
-        "asha.aconfig",
-        "audio_routing.aconfig",
-        "bta_dm.aconfig",
-        "framework.aconfig",
-        "gap.aconfig",
-        "hap.aconfig",
-        "hfp.aconfig",
-        "l2cap.aconfig",
-        "leaudio.aconfig",
-        "rfcomm.aconfig",
-        "system_service.aconfig",
+        "**/*.aconfig",
     ],
 }