Revert of [Android] Rework multidex and enable multidex for unit_tests_apk.

build/config/android/rules.gni

Index: build/config/android/rules.gni
diff --git a/build/config/android/rules.gni b/build/config/android/rules.gni
index fb06814d41e32c41a82f23269fe4fe5361053d58..da9a8536f3ed4f1b791461e5319d06169b2ddb2e 100644
--- a/build/config/android/rules.gni
+++ b/build/config/android/rules.gni
@@ -1484,21 +1484,6 @@
     _srcjar_deps += [ ":${_template_name}__native_libraries_java" ]
   }
 
-  if (!defined(invoker.apk_under_test)) {
-    java_cpp_template("${_template_name}__multidex_config_java") {
-      package_name = "org/chromium/base/multidex"
-      sources = [
-        "//base/android/java/templates/ChromiumMultiDex.template",
-      ]
-
-      defines = []
-      if (enable_multidex) {
-        defines += [ "ENABLE_MULTIDEX" ]
-      }
-    }
-    _srcjar_deps += [ ":${_template_name}__multidex_config_java" ]
-  }
-
   java_target = "${_template_name}__java"
   java_library_impl(java_target) {
     forward_variables_from(invoker, [ "run_findbugs" ])