www/beehive: fix build on riscv64

• bump golang.org/x/sys dependency to a version new enough to support riscv64-freebsd
• remove ONLY_FOR_ARCH; this port should build on any arch that supports Go
• only strip binaries if stripping has been requested

Sponsored by: Berliner Linux User Group e.V.
Approved by: portmgr (build fix blanket)
Differential Revision: https://reviews.freebsd.org/D39157