Cleanup python version properties

Now that python 2 is fully removed, there's no need for
version-specific properties. Remove them.

Also remove usages of embedded_launcher: true, as that
is the new default value.

Bug: 399954452
Test: Presubmits
Change-Id: I368416638bbf1f5e76f7756792d537f72f3c9714

tests/cts/multidevices/Android.bp

@@ -42,9 +42,4 @@ python_test_host {
         // Package the snippet with the mobly test
         ":connectivity_multi_devices_snippet",
     ],
-    version: {
-        py3: {
-            embedded_launcher: true,
-        },
-    },
 }

thread/tests/multidevices/Android.bp

@@ -35,9 +35,4 @@ python_test_host {
         "mts-tethering",
         "general-tests",
     ],
-    version: {
-        py3: {
-            embedded_launcher: true,
-        },
-    },
 }