xi2: Fix incorrect input source type in Input debug message
This drops cursor and eraser source names to account for their removal from GdkInputSource so that GDK_DEBUG=input debug message correctly prints source type in X11 environment.
Fixes: c1d90273 ("gdk: Drop GDK_SOURCE_ERASER")
Fixes: 3285f52d ("gdk: Drop GDK_SOURCE_CURSOR")
Closes: #6619 (closed)
Edited by Hansem Ro