Revert "contextengine: clear invalid ranges if BOM is found"
Revert "contextengine: clear invalid ranges if BOM is found"

This reverts commit 54e48e9c45e0ccef4d8fd8f5b9a8660aa6b0ae0b.

Now that we have other measures in place to protect against BOM,
we can remove this commit which caused all highlighting to be
stopped after the line with the BOM.

GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview,GNOME/gtksourceview