JNI Doc: Remove reference to fixed bug.

Bug: 890452
Change-Id: I06a5603ee5a3ce7ba192112070d76729e674f598
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2128942
Auto-Submit: Darwin Huang <huangdarwin@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755067}

base/android/jni_generator/README.md

@@ -150,11 +150,7 @@ void MyClass::NonStatic(JNIEnv* env) { ... }
 2. Call `JniMocker#mock` in a `setUp()` method for each interface you want to
    stub out.
 
-Note: Mocking native methods doesn't work in tests that are part of APKs that
-use an [`apk_under_test`](https://cs.chromium.org/search/?q=file:BUILD.gn+%22apk_under_test+%3D%22&type=cs).
-[This crbug](http://crbug.com/890452) tracks removing the `apk_under_test` variable.
-
-JniMocker will reset the stubs during `tearDown()`.
+`JniMocker` will reset the stubs during `tearDown()`.
 
 ```java
 /**