Removes all tags in the range between start and end.
Be careful with this function; it could remove tags added in code unrelated to the code you’re currently writing. That is, using this function is probably a bad idea if you have two or more unrelated code sections that add tags.
| this |
a `GtkTextBuffer` |
| start |
one bound of range to be untagged |
| end |
other bound of range to be untagged |