Resolve "[Feature flag] Rollout of `add_ignore_all_white_spaces`"

What does this MR do and why?

Removes the add_ignore_all_white_spaces feature flag.

This feature flag changes the ignore_white_space option to use the git diff option ignore-all-space rather than ignore-space-change.

https://git-scm.com/docs/git-diff#Documentation/git-diff.txt-ignore-space-change

To Test:

Steps to reproduce

1. Add and commit this a file called TESTFILE with the following contents into a repository:

   Leading whitespace with tab 1
   Leading whitespace with space 2
   Trailing whitespace with tab 3
   Trailing whitespace with space 4

2. Make a new branch. Eg. whitespace-test

3. Replace TESTFILE with the following contents (Note the leading/trailing whitespace changes as well):

           Leading whitespace with tab 1
    Leading whitespace with space 2
   Trailing whitespace with tab 3	
   Trailing whitespace with space 4 

4. Create a new MR from this branch.

5. Look at the diff with Show Whitespace changes both on and off, observe that whitespace changes with leading whitespace are not displayed.

Related to #390657 (closed)