Reimplement removal fix-it hints in terms of replace

Reimplement removal fix-it hints in terms of replace

This patch eliminates class fixit_remove, reimplementing
rich_location::add_fixit_remove in terms of replacement with the
empty string.  Deleting the removal subclass simplifies
fixit-handling code, as we only have two concrete fixit_hint
subclasses to deal with, rather than three.

The patch also fixes some problems in diagnostic-show-locus.c for
situations where a replacement fix-it has a different range to the
range of the diagnostic, by unifying the drawing of the two kinds of
fixits.  For example, this:

  foo = bar.field;
      ^
            m_field

becomes:

  foo = bar.field;
      ^
            -----
            m_field

showing the range to be replaced.

gcc/ChangeLog:
	* diagnostic-show-locus.c
	(layout::annotation_line_showed_range_p): New method.
	(layout::print_any_fixits): Remove case fixit_hint::REMOVE.
	Reimplement case fixit_hint::REPLACE to cover removals, and
	replacements where the range of the replacement isn't one
	of the ranges in the rich_location.
	(test_one_liner_fixit_replace): Likewise.
	(selftest::test_one_liner_fixit_replace_non_equal_range): New
	function.
	(selftest::test_one_liner_fixit_replace_equal_secondary_range):
	New function.
	(selftest::test_diagnostic_show_locus_one_liner): Call the new
	functions.
	* diagnostic.c (print_parseable_fixits): Remove case
	fixit_hint::REMOVE.

libcpp/ChangeLog:
	* include/line-map.h (fixit_hint::kind): Delete REPLACE.
	(class fixit_remove): Delete.
	* line-map.c (rich_location::add_fixit_remove): Reimplement
	by calling add_fixit_replace with an empty string.
	(fixit_remove::fixit_remove): Delete.
	(fixit_remove::affects_line_p): Delete.

From-SVN: r239632