Remove stray -modulus option from the ec manual page.

Reviewed-by: Paul Yang <yang.yang@baishancloud.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8082)

(cherry picked from commit d7bcbfd0828616f33008e711eabc6ec00b32e87b)