fish: complete files in more places

[9999years]

Description

Normally, the Fish completion plugin won't complete filenames, which is useful for beet import and similar! This removes the -f (no filename completion) flag from various places in the output.

To Do

• Documentation. (If you've added a new command-line flag, for example, find the appropriate page under docs/ to describe it.)
• Changelog. (Add an entry to docs/changelog.rst to the bottom of one of the lists near the top of the document.)
• Tests. (Very much encouraged but not strictly required.)

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.