gdbus-codegen: Drop DocBook warning tags from generated code
gdbus-codegen: Drop DocBook warning tags from generated code

gtk-doc switched from DocBook to Markdown ages ago. There is no Markdown
equivalent for `<warning>`, so just drop it. It wasn’t adding anything
particularly valuable to the documentation.

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

Fixes: #1130

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib