Revert "Merge branch 'kassio/import-validate-url-before-downloading' into 'master'"

What does this MR do?

This change was causing a bug in the Project templates feature. Project Templates uses the Project Export/Import under the hood, which downloads a Project export from the local server, therefore the added validation blocks the process.

Related to:

• Issue to introduce the validation: #329318 (closed)
• QA issue about the bug: #326586 (closed)
• Infra issue about the tests failures: gitlab-com/gl-infra/production#4410 (closed)
• Issue to track the revert: gitlab-org/release/tasks#2414 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
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Security

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