Convert generate_operator_out to python 3

generate_operator_out already started with
a #!/usr/bin/env python3. Make it use python 3
when built with soong as well.

Bug: 203436762
Test: m libart-compiler and presubmits
Change-Id: I1e6b64231c22283034a7e47335df629014083446
diff --git a/tools/Android.bp b/tools/Android.bp
index 85648e5..b7f5c1b 100644
--- a/tools/Android.bp
+++ b/tools/Android.bp
@@ -28,14 +28,6 @@
     srcs: [
         "generate_operator_out.py",
     ],
-    version: {
-        py2: {
-            enabled: true,
-        },
-        py3: {
-            enabled: false,
-        },
-    },
 }
 
 soong_config_module_type_import {