maint: go back to using ‘error’

maint: go back to using ‘error’

Now that Gnulib’s ‘error’ module does proper static checking
for not returning, we need no longer use the ‘die’ macro.
This makes code easier to read for people that are used to ‘error’.
* cfg.mk (error_fns, exclude_file_name_regexp): Remove ‘die’.
(sc_die_EXIT_FAILURE): Remove.
* src/die.h: Remove.  All includes removed.  All calls to ‘die’
changed back to calls to ‘error’.
* src/install.c (get_ids): Use quoteaf (problem found with
make syntax-check).
* src/system.h: Include error.h, since some of our macros call ‘error’.
Stop including error.h elsewhere.