unnecessary_this 
            
            Don’t access members with this unless avoiding shadowing.
This rule is available as of Dart 2.0.0.
Rule sets: recommended, flutter
This rule has a quick fix available.
Details
From Effective Dart:
DON’T use this when not needed to avoid shadowing.
BAD:
class Box {
  var value;
  void update(new_value) {
    this.value = new_value;
  }
}
GOOD:
class Box {
  var value;
  void update(new_value) {
    value = new_value;
  }
}
GOOD:
class Box {
  var value;
  void update(value) {
    this.value = value;
  }
}
Usage
To enable the unnecessary_this rule,
add unnecessary_this under linter > rules in your
analysis_options.yaml
file:
linter:
  rules:
    - unnecessary_this