[show-hint addon] Drop default max-width for hint widget

Closes codemirror#4080

Author: marijnh

addon/hint/show-hint.css

@@ -16,7 +16,6 @@
   background: white;
   font-size: 90%;
   font-family: monospace;
-  max-width: 19em;
 
   max-height: 20em;
   overflow-y: auto;