Remove pod spec overrides

[amisevsk]

What does this PR do?:

Removes field .spec.podSpecOverrides from the DevWorkspace custom resource definition as added in #872

Which issue(s) this PR fixes:

Following discussion in #920, it may make more sense to support these fields via attributes in order to allow them to included in Devfiles as well as in DevWorkspaces

PR acceptance criteria:

Testing and documentation do not need to be complete in order for this PR to be approved. We just need to ensure tracking issues are opened.

• Open new test/doc issues under the devfile/api repo
• Check each criteria if:
• There is a separate tracking issue. Add the issue link under the criteria
  or
• test/doc updates are made as part of this PR
• If unchecked, explain why it's not needed

• Unit/Functional tests

• QE Integration test

• Documentation

• Client Impact

How to test changes / Special notes to the reviewer:

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: amisevsk, l0rd

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment