_gtkLabelRemove remove a sub string in a Label
object.
Be careful, if the text label contains markup and(or) mnemonic, the supplemental characters are taken off.
Prototype : fun [ObjGtkLabel I I I] ObjGtkLabel
ObjGtkLabel : the Label object.
I : the position where the sub string will be removed.
If the value is negative then the position will be from the end.
I : the length to remove.
I : the flag (it should be the same than defined to _gtkLabelSet
or the last _gtkLabelAdd).
LABEL_SET_SIMPLE (or 0) : the content is basic, without mnemonic or markup;
LABEL_SET_SIMPLE_MNEMONIC : the content is basic and contains a mnemonic;
LABEL_SET_MARKUP : the content has one or more markups;
LABEL_SET_MARKUP_MNEMONIC : the content has a mnemonic and one or more markups;
LABEL_SET_ATTRIBUTES : not implemented yet, don't use at this time.
Return ObjGtkLabel : the same Label object
or nil if an error occurs.