Force-remove temp completion file to coexist with alias rm='rm -i'

[simonm]

Summary

_fifc removes the temporary completion-list file (created via mktemp) at the end of each invocation using a plain rm $_fifc_complist_path. For users who alias rm to rm -i — a common safety habit — that alias injects an interactive confirmation prompt on every completion, breaking the flow.

This change switches that single call to rm -f, which:

• Bypasses the -i confirmation an alias would inject.
• Silently no-ops if the file is already gone, which is harmless here since the path is only used by _fifc itself.

Scope is intentionally minimal: only the cleanup of $_fifc_complist_path in functions/_fifc.fish is touched. No behavior change for users without the alias.

Test plan

• With alias rm='rm -i' set in fish, trigger fifc completion and confirm no confirmation prompt appears and the temp file is removed.
• Without the alias, confirm behavior is unchanged.