Correct a few mislabeled items in LTI 1.3 introduction
Correct a few mislabeled items in LTI 1.3 introduction

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Test Plan:
- Run the `doc:api` rake task
- Navigate to /doc/api/file.lti_dev_key_config.html
- Verify the page loads with the corrected terms

Change-Id: I1ecc43bfa90e4b6f2349c31a15cad28480f6dbea
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/247864
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: Weston Dransfield <e9203059795dc94e28a8831c65eb7869e818825e@instructure.com>
Product-Review: Weston Dransfield <e9203059795dc94e28a8831c65eb7869e818825e@instructure.com>
Reviewed-by: Mysti Lilla <431d062aff1e8f25416b3a7b732fe6effdb03f9a@instructure.com>

instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms