I looked at the macro expansion of the form you wrote and it looks like gibberish, so I don't think the :hook keyword allows expressions to be used as hooks, you need to define a function and use the function name:

(use-package pascal ; presumably
  :init
  (defun remove-pascal-completions ()
    (remove-hook 'completion-at-point-functions
                 'pascal-completions-at-point t))
  :hook (pascal-mode . remove-pascal-completions))

Also, the weird single quote character you used probably doesn't work in Emacs (but maybe you have normal single quotes in your file and it's just lemmy's markdown messing things up).