simplify configs

- use POWERLEVEL9K_ICON_PADDING instead of
  POWERLEVEL9K_VISUAL_IDENTIFIER_EXPANSION to customize padding after
  icons
- remove reliance on UTF-8 locale when the config is being sourced

config/p10k-pure.zsh

@@ -25,11 +25,12 @@
 () {
   emulate -L zsh
 
-  autoload -Uz is-at-least && is-at-least 5.1 || return
-
   # Unset all configuration options.
   unset -m 'POWERLEVEL9K_*'
 
+  # Zsh >= 5.1 is required.
+  autoload -Uz is-at-least && is-at-least 5.1 || return
+
   # Prompt colors.
   local grey=242
   local red=1