ci: use go 1.16 everywhere

[jackfrancis]

Reason for Change:

This PR rationalizes the various go CI to use 1.16 everywhere.

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[jackfrancis]

I wasn't able to find any reason to keep this hidden file around

[mboersma]

Maybe it was to support goenv? I used to use that, and I'm the only commiter on that file. 👍🏻 to deleting it.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@7ca2a31). Click here to learn what that means.
The diff coverage is 38.28%.

@@            Coverage Diff            @@
##             master    #4528   +/-   ##
=========================================
  Coverage          ?   72.05%           
=========================================
  Files             ?      141           
  Lines             ?    21765           
  Branches          ?        0           
=========================================
  Hits              ?    15682           
  Misses            ?     5131           
  Partials          ?      952           

Impacted Files	Coverage Δ
cmd/rotatecerts/arm.go	0.00% <0.00%> (ø)
cmd/rotate_certs.go	11.03% <11.03%> (ø)
cmd/scale.go	12.56% <12.37%> (ø)
cmd/addpool.go	17.97% <17.97%> (ø)
cmd/update.go	23.07% <23.07%> (ø)
cmd/upgrade.go	35.92% <25.00%> (ø)
cmd/get_logs.go	49.57% <49.57%> (ø)
cmd/get_skus.go	50.63% <50.63%> (ø)
cmd/root.go	56.28% <52.63%> (ø)
cmd/generate.go	50.41% <54.54%> (ø)
... and 7 more

---

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[mboersma]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, mboersma

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