sysutils/container-diff: fix build on riscv64

Bump golang.org/x/sys dependency to a version new enough to support
riscv64-freebsd. Remove patch obsoleted through this change.

Sponsored by: Berliner Linux User Group e.V.
Approved by: portmgr (build fix blanket)
Differential Revision: https://reviews.freebsd.org/D39043