Undeprecate query extension

[philvarner]

Related Issue(s):

• Is Query Extension (STACQL) still going to be deprecated? #242

Proposed Changes:

1. remove deprecated language for Query Extension

PR Checklist:

• This PR is made against the dev branch (all proposed changes except releases should be against dev, not master).
• This PR has no breaking changes.
• This PR does not make any changes to the core spec in the stac-spec directory (these are included as a subtree and should be updated directly in radiantearth/stac-spec)
• I have added my changes to the CHANGELOG or a CHANGELOG entry is not required.

[m-mohr]

Shouldn't it move to a separate repo instead?

[philvarner]

Shouldn't it move to a separate repo instead?

I think we should move some (if not all) of them to a separate repo, but this is just to update it so it's accurate.