lib: delete PS1 default

A default PS1 doesn't make sense: the user will either choose a theme or not
care about a default prompt since they can set it themselves.

Fixes #7054

lib/theme-and-appearance.zsh

@@ -45,9 +45,6 @@ setopt prompt_subst
 
 [[ -n "$WINDOW" ]] && SCREEN_NO="%B$WINDOW%b " || SCREEN_NO=""
 
-# Apply theming defaults
-PS1="%n@%m:%~%# "
-
 # git theming default: Variables for theming the git info prompt
 ZSH_THEME_GIT_PROMPT_PREFIX="git:("         # Prefix at the very beginning of the prompt, before the branch name
 ZSH_THEME_GIT_PROMPT_SUFFIX=")"             # At the very end of the prompt