strbuf.c: remove unused function

strbuf_tolower() is not used anywhere.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

strbuf.c

@@ -91,13 +91,6 @@ void strbuf_ltrim(struct strbuf *sb)
 	sb->buf[sb->len] = '\0';
 }
 
-void strbuf_tolower(struct strbuf *sb)
-{
-	int i;
-	for (i = 0; i < sb->len; i++)
-		sb->buf[i] = tolower(sb->buf[i]);
-}
-
 struct strbuf **strbuf_split(const struct strbuf *sb, int delim)
 {
 	int alloc = 2, pos = 0;

strbuf.h

@@ -81,7 +81,6 @@ extern void strbuf_trim(struct strbuf *);
 extern void strbuf_rtrim(struct strbuf *);
 extern void strbuf_ltrim(struct strbuf *);
 extern int strbuf_cmp(const struct strbuf *, const struct strbuf *);
-extern void strbuf_tolower(struct strbuf *);
 
 extern struct strbuf **strbuf_split(const struct strbuf *, int delim);
 extern void strbuf_list_free(struct strbuf **);