Don't use hermetic go environment for installing godep

[cblecker]

What type of PR is this?
/kind bug

What this PR does / why we need it:
This is unneeded, and causes this build environment to persist throughout the lifetime of any godep script.

This now uses the same method that we use for installing gazelle and other utilities from vendor.

Does this PR introduce a user-facing change?:

NONE

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cblecker

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[ixdy]

/lgtm

Thanks!

[ixdy]

cc @apelisse
(the behavior is changing back to what it used to be)

[fejta-bot]

/retest
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Review the full test history for this PR.

Silence the bot with an /lgtm cancel comment for consistent failures.

[ixdy]

/retest

[cblecker]

/retest

[k8s-ci-robot]

@cblecker: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
pull-kubernetes-e2e-kops-aws	b1aae87	link	/test pull-kubernetes-e2e-kops-aws

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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