fold: Remove div_if_zero_remainder [PR122437]

fold: Remove div_if_zero_remainder  [PR122437]

While looking into something related to fold-const.cc, I noticed
that div_if_zero_remainder was unused. The last use of it was
removed in r5-3374-gf65586dcd19846 (via the removal of try_move_mult_to_index),
over 11 years ago.  So it is time to remove this unused function too.
Plus this function is just a small wrapper around wi::multiple_of_p but
creating trees which can get expensive so folks should use wi::multiple_of_p
directly instead.

Bootstrapped and tested on x86_64-linux-gnu.

	PR tree-optimization/122437
gcc/ChangeLog:

	* fold-const.cc (div_if_zero_remainder): Remove.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>