Update modifier variable docs (#5114)

Listing the potential key combination in a single line is hard to read and also redundant when we have the same information in the table below.

editions/tw5.com/tiddlers/variables/modifier Variable.tid

@@ -5,7 +5,7 @@ title: modifier Variable
 type: text/vnd.tiddlywiki
 
 Within the ''action'' string of the DroppableWidget, the ''action'' string of the ButtonWidget and the ''action'' string of the LinkCatcherWidget and the EventCatcherWidget, the <<.def modifier>> [[variable|Variables]] contains the modifier key(s) held during the drag-process.
-The possible keys are ''meta'', ''ctrl'', ''shift'', ''alt'', ''meta'' and ''ctrl'', ''meta'' and ''shift'', ''meta'' and ''alt'', ''ctrl'' and ''shift'', ''alt'' and ''shift'', ''ctrl'' and ''alt'', ''ctrl'' and ''alt'' and ''shift'', ''meta'' and ''alt'' and ''shift'', ''meta'' and ''ctrl'' and ''shift'', ''meta'' and ''ctrl'' and ''alt'', ''meta'' and ''ctrl'' and ''alt'' and ''shift''
+Possible key combinations are listed in the table below.
 
 The variable contains a string that identifies the keys: