dex.py: Remove obsolete flags, code clean-up.

Change-Id: I20d7316522446b934583fb23ff34f9212b0fb346
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1694090
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Sam Maier <smaier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676101}

build/config/android/internal_rules.gni

@@ -1300,13 +1300,11 @@ if (enable_java_templates) {
           invoker.output,
         ]
 
-        _rebased_output = rebase_path(invoker.output, root_build_dir)
-
         args = [
           "--depfile",
           rebase_path(depfile, root_build_dir),
-          "--dex-path",
-          _rebased_output,
+          "--output",
+          rebase_path(outputs[0], root_build_dir),
         ]
 
         if (_proguard_enabled) {
@@ -1327,7 +1325,7 @@ if (enable_java_templates) {
 
         if (defined(invoker.input_dex_classpath)) {
           inputs += [ invoker.build_config ]
-          args += [ "--inputs=@FileArg(${invoker.input_dex_classpath})" ]
+          args += [ "--input-list=@FileArg(${invoker.input_dex_classpath})" ]
         }
 
         inputs += _dexing_jars