Revert "Disable company exclusively on Nix"

This reverts commit 53b4fffbee.

config.el

@@ -49,8 +49,8 @@
               (message "No Compilation Errors!")))))
 ;; Enable writeroom for text modes
 (setq writeroom-major-modes '(markdown-mode org-mode))
-;; Disable company in Nix mode
-(set-company-backend! 'nix-mode nil)
+;; Speed up company mode
+(setq company-idle-delay nil)
 ;; Use Microsoft's python language server by default
 (after! lsp-python-ms
   (set-lsp-priority! 'mspyls 1))