x11/libX11: update to 1.7.0

Changes: https://lists.x.org/archives/xorg-announce/2020-November/003065.html
PR: 255770
Reported by: portscout
Approved by: zeising
Exp-run by: antoine
Differential Revision: https://reviews.freebsd.org/D30202

(cherry picked from commit ee545c31194e74fd0f6c484723b965e4bcaa0446)