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.

.conduit.yaml

@@ -28,7 +28,7 @@
 - repo:
     - https://github.com/zsh-users/zsh-autosuggestions.git
     - https://github.com/zsh-users/zsh-history-substring-search.git
-    - https://github.com/zdharma/fast-syntax-highlighting.git
+    - https://github.com/zsh-users/zsh-syntax-highlighting.git
     - https://github.com/junegunn/fzf.git
 - command:
     - fzf/install --bin