Remove unused "prefix" variable in prompt presets

[ci skip]

share/tools/web_config/sample_prompts/classic_vcs.fish

@@ -8,7 +8,6 @@ function fish_prompt --description 'Write out the prompt'
 
     # Color the prompt differently when we're root
     set -l color_cwd $fish_color_cwd
-    set -l prefix
     set -l suffix '>'
     if contains -- $USER root toor
         if set -q fish_color_cwd_root

share/tools/web_config/sample_prompts/informative_vcs.fish

@@ -57,7 +57,6 @@ function fish_prompt --description 'Write out the prompt'
     end
 
     set -l color_cwd
-    set -l prefix
     set -l suffix
     switch "$USER"
         case root toor