sysutils/gcp-ops-agent: Update to 2.48.0 and return to pool

Release Notes: https://github.com/GoogleCloudPlatform/ops-agent/releases/tag/2.48.0

Background:

I added this port at a user's request, pending their run-time feedback.
The user became unresponsive, and I do not use Google Compute Engine or
ops-agent, so returning to the pool. If unclaimed within a month or so,
I will mark it as DEPRECATED.

Current status:

The port builds successfully and does not crash with a simple run-time
test.

Sponsored by: The FreeBSD Foundation