MathQuill: removing a redundant instance and fixing a bug with editing powers and ENTER... however, there are exceptions still in Chrome

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@23540 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
set center: progressIndicator

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@23541 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e