Remove header filter from localisation grid field

[satrun77]

Description

Manual testing steps

Issues

• Search in Localisation tab does not work  #875

Pull request checklist

• The target branch is correct
  • See picking the right version
• All commits are relevant to the purpose of the PR (e.g. no debug statements, unrelated refactoring, or arbitrary linting)
  • Small amounts of additional linting are usually okay, but if it makes it hard to concentrate on the relevant changes, ask for the unrelated changes to be reverted, and submitted as a separate PR.
• The commit messages follow our commit message guidelines
• The PR follows our contribution guidelines
• Code changes follow our coding conventions
• This change is covered with tests (or tests aren't necessary for this change)
• Any relevant User Help/Developer documentation is updated; for impactful changes, information is added to the changelog for the intended release
• CI is green

[tractorcow]

Incorrect target branch?

[satrun77]

Incorrect target branch?

I targeted 7.1. Which branch do you want it to be?

[tractorcow]

No that's ok, I just saw lots of unrelated commit messages. It seems fine now.

[satrun77]

No that's ok, I just saw lots of unrelated commit messages. It seems fine now.

Ah yes. I saw that and rebased before I saw your comment :) Thanks for looking into this PR

[tractorcow]

fixed and thanks for the contribution.

[GuySartorelli]

Didn't see this PR in time - but it should probably be conditional on whether BasicSearchContext is available (i.e. whether framework 5.2+ is used) - see https://docs.silverstripe.org/en/5/developer_guides/forms/using_gridfield_with_arbitrary_data/#arraydata-filter