fix: remove mockProps and wrapper from fileters Robots

[timothyrusso]

Remove mockProps and wrapper from 'fileters Robots' in the MainPage.test.js

These values are not needed because are already defined in the beforeEach():

beforeEach(() => {
  const mockProps = {
    onRequestRobots: jest.fn(),
    robots: [],
    searchField: '',
    isPending: false
  }
  wrapper = shallow(<MainPage {...mockProps}/>)
 })