spec: Use Requires: git-core if distribution is new enough

[cgwalters]

I am planning to propose we include origin-clients in Fedora Atomic
Workstation by default.

It was pointed out that that pulls in git which pulls in Perl. A
while ago we added a git-core which is really all we need:
https://bugzilla.redhat.com/show_bug.cgi?id=1161251

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[jlebon]

Can someone take a look at this? It seems minor, though it'd make origin-clients even more attractive for folks trying to keep a minimal base OS.

[openshift-bot]

/test cross

[dustymabe]

/retest

[openshift-ci-robot]

@cgwalters: The following tests failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
ci/openshift-jenkins/extended_networking_minimal	cb73679	link	/test extended_networking_minimal
ci/openshift-jenkins/cross	cb73679	link	/test cross
ci/prow/gcp	cb73679	link	/test gcp
ci/prow/cross	cb73679	link	/test cross

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[openshift-bot]

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Mark the issue as fresh by commenting /remove-lifecycle stale.
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/lifecycle stale

[jlebon]

Looks like we can close this? The dep was completely dropped in #19509.