Started just wanting to fix the "gtk-strikethrough" icon,
but kept finding items marked deprecated.
This change may be incomplete, but all changes were to deprecated
icons (that used to be "stock", I think).
Icon name candidates were identified by extracting all used icon-name
values and checking which existed in my system's copy of the 'breeze' theme.
If missing, these were checked online to find the new replacement.
(I couldn't find an authoritative list of the replacements,
but looking each up finds the right deprecation warning)
