Drop fast-syntax-highlighting due to being wrong

When using `git` aliases, the alias would be highlighted red by
fast-syntax-highlighting even though the alias is valid so remove it and
go back to zsh-syntax-highlighting instead.

zshrc

@@ -19,8 +19,7 @@ ZSH_AUTOSUGGEST_ACCEPT_WIDGETS=(end-of-line vi-end-of-line)
 source-plugin zsh-history-substring-search
 
 # Command syntax highlighting
-source-plugin fast-syntax-highlighting
-fast-theme -q ~/.config/zsh/fresh.ini
+source-plugin zsh-syntax-highlighting
 
 # Automatically source .enter and .exit scripts on cd
 source-plugin autoenv