Remove kotlin.RequiresOptIn

Which is now enabled by default.

Bug: 253772249
Test: Presubmit
Change-Id: Ida4e35235c0bc0be973634988b037dec0ad829bc
diff --git a/tests/spa_unit/Android.bp b/tests/spa_unit/Android.bp
index 0678168..da33411 100644
--- a/tests/spa_unit/Android.bp
+++ b/tests/spa_unit/Android.bp
@@ -44,7 +44,6 @@
     ],
     kotlincflags: [
         "-Xjvm-default=all",
-        "-opt-in=kotlin.RequiresOptIn",
     ],
 
     instrumentation_for: "Settings-core",