drm/amd/amdgpu_dm/mst: Remove unneeded edid assignment when destroying connectors

Doesn't do anything, noticed this while cleaning up some unrelated
stuff.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200331205740.135525-2-lyude@redhat.com


Reviewed-by: Alex Deucher <alexdeucher@gmail.com>