fix most staticcheck warnings

[gfr10598]

This PR fixes most of the warnings issued by the staticcheck tool.
There are a few warnings left, primarily for unused err values.

Testing:
Successful build + unit test coverage should be adequate, since these are expected to be strict refactorings and dead code deletions.
Test coverage stats should be checked to ensure modified lines are actually covered by unit tests.

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This change is 

[coveralls]

Pull Request Test Coverage Report for Build 6422

• 33 of 72 (45.83%) changed or added relevant lines in 12 files are covered.
• 5 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.2%) to 62.69%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cmd/etl_worker/etl_worker.go	19	20	95.0%
cmd/generate_schema_docs/main.go	0	1	0.0%
etl/globals.go	2	3	66.67%
parser/annotation.go	0	1	0.0%
storage/rowwriter.go	4	5	80.0%
schema/pt_schema.go	0	2	0.0%
web100/tcpkis.go	0	2	0.0%
parser/ss.go	0	3	0.0%
schema/web100.go	0	3	0.0%
parser/pt.go	6	14	42.86%

Files with Coverage Reduction	New Missed Lines	%
parser/pt.go	1	75.33%
schema/web100.go	1	0%
active/poller.go	3	67.86%

Totals
Change from base Build 6411:	0.2%
Covered Lines:	3468
Relevant Lines:	5532

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💛 - Coveralls

[SaiedKazemi]

Reviewed 36 of 38 files at r1.
Reviewable status: 1 change requests, 0 of 1 approvals obtained (waiting on @gfr10598)

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fake/fold.go, line 103 at r1 (raw file):

	}
	return len(t) >= 0

This doesn't look correct to me. If len(t) is 1, the old code returns false but this code returns true. Right?

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storage/rowwriter.go, line 29 at r1 (raw file):

	o stiface.ObjectHandle

	// this attribute struct can be used to accumulate attributes that

Nit: can you capitalize? Go Style Decision: "Comments that are complete sentences should be capitalized and punctuated like standard English sentences."

[gfr10598]

Reviewable status: 1 change requests, 0 of 1 approvals obtained (waiting on @gfr10598)

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fake/fold.go, line 103 at r1 (raw file):

	}
	return len(t) >= 0

True enough - and no test coverage. 8-(

[stephen-soltesz]

Closing this PR to clean up old PRs - the work to normalize the ETL codebases with standard Go static checks can be tracked in #1081