mgr/dashboard: rm warning/error threshold for cpu usage

mgr/dashboard: rm warning/error threshold for cpu usage

for multi-core cpu's the value can be more than 100% so it doesn't make
sense to show warning/error when the usage is at or more than 100%.
hence removing it

Fixes: https://tracker.ceph.com/issues/58838
Signed-off-by: Nizamudeen A <nia@redhat.com>
(cherry picked from commit 131a70754a6bfbbb2d1481ba74436953c6ecc226)

 Conflicts:
	src/pybind/mgr/dashboard/frontend/src/app/shared/components/usage-bar/usage-bar.component.html
  - some changes are not in quincy for the threasholds. so adapting it