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>

libc/include/sprinter.h

@@ -113,8 +113,7 @@ static inline void sprinter_page_w2(uint8_t page) { _io_page_w2 = page; }
 static inline void sprinter_page_w3(uint8_t page) { _io_page_w3 = page; }
 
 /* ---- Sprinter-specific debug helpers ------------------------------ */
-/* Print one byte as two uppercase hex digits via putchar(). */
-void print_hex(uint8_t v);
+/* Use hex8() / hex16() / hex32() from <stdio.h> for hex debug output. */
 
 #ifdef DEBUG_RT
 /*