build: Drop autotools support

So long, and thanks for everything. We’re a Meson-only shop now.

glib-2-58 will remain the last stable GLib release series which is
buildable using autotools.

We continue to install autoconf macros for autotools-using projects
which depend on GLib; they are stable API.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

gio/gdbus-2.0/codegen/Makefile.am

@@ -1,28 +0,0 @@
-include $(top_srcdir)/glib.mk
-
-bin_SCRIPTS =
-
-codegendir = $(datadir)/glib-2.0/codegen
-codegen_PYTHON =						\
-	__init__.py						\
-	codegen.py						\
-	codegen_main.py						\
-	codegen_docbook.py					\
-	config.py						\
-	dbustypes.py						\
-	parser.py						\
-	utils.py						\
-	$(NULL)
-
-CLEANFILES += config.pyc
-
-bin_SCRIPTS += gdbus-codegen
-CLEANFILES += gdbus-codegen
-EXTRA_DIST += gdbus-codegen.in
-
-gdbus-codegen: gdbus-codegen.in Makefile $(codegen_PYTHON)
-	$(AM_V_GEN) sed -e 's,@DATADIR\@,$(datadir),' -e 's,@PYTHON\@,$(PYTHON),' $< > $@.tmp && mv $@.tmp $@
-	@chmod a+x $@
-
-clean-local:
-	rm -f *~