Remove unneeded static imports

google-java-format removes some but not all unneeded import statements.
I suggest that it should remove more unneeded static imports.

As an example, in Error Prone file `ASTHelpers.java`, consider [the line](https://github.com/google/error-prone/blob/1c38087e16210e1a4b739cb6a21565fc283e8532/check_api/src/main/java/com/google/errorprone/util/ASTHelpers.java#L27)

```java
import static com.google.errorprone.util.ASTHelpers.isStatic;
```

This is unnecessary because it is statically importing a method defined in the same file.

It would be nice if google-java-format removed the line.