build: remove trailing blank lines; enable the syntax-check rule

* cfg.mk (disable_temporarily): Remove sc_prohibit_trailing_blank_lines.
* appliance/Makefile.am: Remove trailing blank line(s).
* appliance/debian/modules/y0_install-guestfsd: Likewise.
* appliance/make.sh.in: Likewise.
* appliance/packagelist.in: Likewise.
* appliance/update.sh.in: Likewise.
* haskell/run-bindtests: Likewise.
* ocaml/run-bindtests: Likewise.
* python/run-python-tests: Likewise.
* recipes/squashfs.example: Likewise.
* ruby/run-ruby-tests: Likewise.