Removed part of fish global completion doc after fish-shell fix

[volkov]

In fish-shell/fish-shell#8442 global completion was fixed, so we don't need workaround anymore

[codecov-commenter]

Codecov Report

Base: 80.59% // Head: 80.59% // No change to project coverage :thumbsup:

Coverage data is based on head (d70b9f2) compared to base (ed82421). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #398 +/- ## ======================================== Coverage 80.59% 80.59% ======================================== Files 6 6 Lines 737 737 ======================================== Hits 594 594 Misses 143 143 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andrey+Kislyuk). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andrey+Kislyuk)

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[kislyuk]

Thanks.