Removed old docs about global developer keys
Removed old docs about global developer keys

fixes PLAT-5655

Change-Id: I0b6111ce31889b69a762fe42a98da0778a91af3a
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/236460
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Xander Moffatt <27f70fe194da423604e6e0a63a3de19814736fa9@instructure.com>
QA-Review: Xander Moffatt <27f70fe194da423604e6e0a63a3de19814736fa9@instructure.com>
QA-Review: Ryan Hawkins <867bc579926fa7e8ba296eacccde2d03d9fb556c@instructure.com>
Product-Review: Karl Lloyd <4c8060af93345c2cc416ee6aa55bceec4e5cc9d4@instructure.com>

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