Remove `C-x n d` as binding to `tuareg-narrow-to-phrase`

[mattiase]

C-x n d currently elicits the warning:

‘tuareg-narrow-to-phrase’ is an obsolete command (as of Apr 10, 2019); use ‘narrow-to-defun’ instead.

There is no point in binding C-x n d to tuareg-narrow-to-phrase since that key sequence is by default bound to narrow-to-defun, of which tuareg-narrow-to-phrase is an obsolete alias.

[mattiase]

Fixed in cd86e73b1ff04222043f685e635c988f182368dd.