Move scripts to python3

Today we are in a limbo where some scripts are run with
python (which defaults to python2 on some systems) some
other with python3. This normalizes everything* to python3.
In the process of doing so:
 - Fixed a sorting issue in gen_bazel and gen_android_bp,
   as it was causing different outputs when running with
   the two different versions of python.
 - Got rid of some vestigial scripts we no longer use.
 - Got rid of the shebang from some scripts that are executed
   only by GN. Having a shebang is misleading because in reality
   GN is the one deciding which version of python to run.

I left only few others that are too expensive to test
right now like some infra bots and the heap profile tools.

Change-Id: Iab5b28196c5a92603745a0dccad17831c43ee590
diff --git a/Android.bp b/Android.bp
index 948d3a9..9c7df36 100644
--- a/Android.bp
+++ b/Android.bp
@@ -258,10 +258,10 @@
   ],
   version_script: "src/profiling/memory/heapprofd_client_api.map.txt",
   stubs: {
-    symbol_file: "src/profiling/memory/heapprofd_client_api.map.txt",
     versions: [
       "S",
     ],
+    symbol_file: "src/profiling/memory/heapprofd_client_api.map.txt",
   },
 }