Drop print_hex.c — replaced by hex8() from hex_print.c

print_hex(uint8_t) was an early bare-metal helper doing exactly what
hex8() in the freshly-ported hex_print.c does (two-digit hex via
putchar()).  hex8() is smaller (asm cp/sbc/daa nibble trick, no LUT)
and consistent with the dec8/hex16/dec16/hex32/dec32 family.

  • Replaced print_hex() calls with hex8() in examples/banked and
    examples/bankedbg.
  • Removed libc/stdio/print_hex.c, dropped its prototype from
    sprinter.h and its entry from lib/Makefile.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/Makefile

@@ -36,7 +36,7 @@ LIBC_C := \
     libc/gfx/gfx_256.c        libc/gfx/gfx_16.c \
     libc/gfx/gfx_font.c       libc/gfx/gfx_text_256.c \
     libc/gfx/gfx_text_16.c \
-    libc/stdio/getchar.c libc/stdio/print_hex.c \
+    libc/stdio/getchar.c \
     libc/stdio/putchar.c libc/stdio/puts.c libc/stdio/file.c \
     libc/stdio/hex_print.c libc/stdio/dec_print.c \
     libc/stdio/solid_helpers.c \