[truetype] Remove Infinality for good.

Remove everything `#ifdef TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY`,
which was undefined for a while now.

* include/freetype/internal/tttypes.h: Ditto.
* src/truetype/truetype.c: Ditto.
* src/truetype/ttdriver.c: Ditto.
* src/truetype/ttgload.c: Ditto.
* src/truetype/ttinterp.c: Ditto.
* src/truetype/ttinterp.h: Ditto.
* src/truetype/ttobjs.c: Ditto.
* src/truetype/ttsubpix.[ch]: Remove files.
* src/truetype/rules.mk: Don't mention "ttsubpix.c".