Remove Agent 5 conditional imports

[mgarabed]

What does this PR do?

Reduce try/except blocks which were guarding against Agent 5 usage. Since Agent 5 is currently on a separate branch, these guards are no longer necessary.

Motivation

Code cleanup.

Additional Notes

There are some #TODOs in datadog_checks/base/checks/base.py which also look ripe for removal, but its not clear how much of the stanzas are specific to Agent 5.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[codecov]

Codecov Report

Merging #5322 into master will decrease coverage by 0.65%.
The diff coverage is 71.42%.

Impacted Files	Coverage Δ
...dog_checks_base/datadog_checks/base/checks/base.py	80.16% <ø> (ø)	⬆️
datadog_checks_base/datadog_checks/base/config.py	100% <ø> (ø)	⬆️
...ase/datadog_checks/base/utils/subprocess_output.py	0% <0%> (ø)	⬆️
...checks_base/datadog_checks/base/checks/__init__.py	100% <100%> (+14.28%)	⬆️
.../datadog_checks/base/checks/prometheus/__init__.py	100% <100%> (ø)	⬆️
datadog_checks_base/tests/conftest.py	33.33% <0%> (-66.67%)	⬇️
datadog_checks_dev/datadog_checks/dev/docker.py	45.76% <0%> (-17.1%)	⬇️
...atadog_checks_base/datadog_checks/base/__init__.py	73.33% <0%> (-13.34%)	⬇️
datadog_checks_base/tests/test_http.py	88.96% <0%> (-9.25%)	⬇️
datadog_checks_base/tests/test_winpdh.py	90.9% <0%> (-6.82%)	⬇️
... and 133 more

[ofek]

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