code: public function deleteSetter($key)
      {
          $pattern = "/^(export\h)?\h*{$key}=.*\n/m";
          $this->buffer = preg_replace($pattern, null, $this->buffer);
  
          return $this;
      }
docs: Delete one setter in buffer
  
  @param  string $key
  
  @return DotenvWriter