don't copy lti_context_id on course reset

fixes: CNVS-13662

**test plan
1. Add lti tool launch to course
2. launch lti tool in course
3. navigate to course settings and reset course content
4. course should reset, lti_context_id should not be set

Change-Id: I2e541e9c6919d996b13160f4e021baf273a4cd22
Reviewed-on: https://gerrit.instructure.com/36564
Reviewed-by: Brad Humphrey <brad@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Brandon Broschinsky <brandonbr@instructure.com>