Remove fixmystreet-mobile references

[jonkri]

The fixmystreet-mobile app has been replaced by the PWA app.

• [ ] Has the code POD documentation been added or updated?
• [ ] Whether this PR should include changes to any public documentation, or the FAQ;
• [x] All cobrand-specific commits start their commit message with the cobrand in square brackets;
• [ ] Is new functionality tested? CodeCov will warn you about the diff coverage, but won’t complain about e.g. new files;
• [ ] Will cobrand-specific changes require additional work to ensure consistent behaviour on www.fixmystreet.com?
• [ ] Are the changes tested for accessibility?
• [ ] Have you updated the changelog? If this is not necessary, put square brackets around this: [skip changelog]

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 72.86%. Comparing base (9c90530) to head (d26cade).

:exclamation: There is a different number of reports uploaded between BASE (9c90530) and HEAD (d26cade). Click for more details.

HEAD has 23 uploads less than BASE

| Flag | BASE (9c90530) | HEAD (d26cade) | |------|------|------| ||25|2|

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5061 +/- ## ========================================== - Coverage 82.62% 72.86% -9.76% ========================================== Files 395 337 -58 Lines 30869 24901 -5968 Branches 4891 4727 -164 ========================================== - Hits 25505 18145 -7360 - Misses 3918 5283 +1365 - Partials 1446 1473 +27 ```

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[jonkri]

@dracos: Done, thank you!