libtextstyle: Assume a working <stdbool.h>.

libtextstyle: Assume a working <stdbool.h>.

* libtextstyle/lib/textstyle.h: Include <stdbool.h> instead of
<textstyle/stdbool.h>.
* libtextstyle/lib/Makefile.am (nobase_nodist_include_HEADERS): Don't add
textstyle/stdbool.h.
(textstyle/stdbool.h): Remove rule.
(BUILT_SOURCES, MOSTLYCLEANFILES, CLEANFILES): Update accordingly.
(EXTRA_DIST): Remove stdbool.mini.h.
* libtextstyle/lib/stdbool.mini.h: Remove file.
* gettext-tools/src/Makefile.am (textstyle/stdbool.h): Remove target.
(BUILT_SOURCES, MOSTLYCLEANFILES): Remove textstyle/stdbool.h.