I cleaned the whole project by deleting local directories like ~/.gradle, ~/.m2 ~./android and ~/workspace/project/.gradle and chosing File -> Invalidate Caches / Restart... in Android Studio.
Now execution of the command ./gradlew leads to the following output:
usr$ ./gradlew tasks
Error: Could not find or load main class org.gradle.wrapper.GradleWrapperMain
Needless to say, I deleted too much, the question is how can it be repaired again? Do you have any ideas how to fix this?