sysutils/oc: fix build and enable on other architectures

Fix build on riscv64 by updating golang.org/x/sys dependency
to a version new enough to support riscv64-freebsd. Remove
GH_TUPLE entries for dependencies already vendored in
upstream's main repository. Only strip if requested.

Sponsored by: Berliner Linux User Group e.V.
Approved by: portmgr (build fix blanket)