perf(dotfiles): remove defunct bind feature detection for fish

[kidonng]

This was originally included in #265 to detect support for bind -M, but versions not supporting the feature were long archaic, and the detection practically becomes if true:

$ codespace:/> fish --version
fish, version 3.1.0
$ codespace:/> bind -M insert # By default there's no mode-specific bindings
$ codespace:/> if bind -M insert &> /dev/null; echo true; end
true

It also has a small cost for users with considerable mode-specific bindings, e.g. with fish_vi_key_bindings enabled:

$ time bind -M insert &> /dev/null

________________________________________________________
Executed in    1.34 millis    fish           external 
   usr time  541.00 micros  541.00 micros    0.00 micros 
   sys time  492.00 micros  492.00 micros    0.00 micros

(Note in this very case it's just ~1ms, but this check is prevalent and can add up. I'd like to address this in other programs too.)