Removing the "javadoc" task from the output of `./gradlew tasks`

AndroidX doesn't use it; presumably nobody else does either

Bug: 127488272

Change-Id: Id2947c3ecb40791aa4bb2c0865960cf39cbb6723
diff --git a/emoji-compat/build.gradle b/emoji-compat/build.gradle
index 7c9d5f0..34acb79 100644
--- a/emoji-compat/build.gradle
+++ b/emoji-compat/build.gradle
@@ -70,3 +70,7 @@
         builtBy rename
     }
 }
+
+// The "javadoc" task is unused so we don't want it to appear in the output of `./gradlew tasks`
+// So, we set the group to null
+tasks["javadoc"].group = null