delete_text
Description:
Deletes a sequence of characters from the buffer.
n_chars characters are deleted starting at position. If n_chars is negative, then all characters until 
      the end of the text are deleted.
If position or n_chars are out of bounds, then they are coerced to sane values.
Note that the positions are specified in characters, not bytes.
Parameters:
| this | 
           a `GtkEntryBuffer`  | 
      
| position | 
           position at which to delete text  | 
      
| n_chars | 
           number of characters to delete  | 
      
Returns:
| 
           The number of characters deleted.  |