As the FSF advises, 'There is no legal significance to using the
three-character sequence “(C)”, but it does no harm.' It does take up
space though! For that reason, we remove it here from our C files.
shared library and places the definitions in a C-only module.
Thanks to Thomas Wawrzinek for this, too!
* box-dynamic/box.c, box/box.c, box-dynamic-module/box.c,
box-module/box.c (mark_box): Fixed typo in comment.