Rename User Settings Feature Preview heading
Rename User Settings Feature Preview heading

This commit renames Feature Preview to Feature Settings, since
the User Settings page will never have any preview features
to be enforced.

CLOSES: FOO-2179
flag=none

Test plan:
- The user settings page has a heading named Feature Settings

Change-Id: Ia191041f60b8b3b9276dbc0444691269ee24390c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/268803
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Product-Review: Erin Hallmark <2a4b17b11682b229726079a631360cf016a43450@instructure.com>
Product-Review: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>
Reviewed-by: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>
QA-Review: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>

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