FIx the android-interop-testing/src/main/res/layout/activity_tester.xml file to get rid of linter messages

[sanjaypujare]

PR #8821 addresses the android linter issue (seen internally in Google3 builds) by adding the tools:ignore="OnClick" property to the elements. However this might not be correct and the issue could be the line 5

    tools:context=".MainActivity"

This may need to be changed in order to run properly in Google3 as suggested by @ejona86