Remove sprintf

Remove sprintf as if you can't easily use snprintf then you probably
have buffer overflow.

Change-Id: Ic4570e099a52d743aca938a2bfadb95981adc503
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/4280
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/include/string.h

@@ -16,7 +16,6 @@ void *memset(void *s, int c, size_t n);
 int memcmp(const void *s1, const void *s2, size_t n);
 void *memchr(const void *s, int c, size_t n);
 #if !defined(__PRE_RAM__)
-int sprintf(char * buf, const char *fmt, ...);
 int snprintf(char * buf, size_t size, const char *fmt, ...);
 #endif