MINOR: buffers: remove b_putstr()

It's not needed anymore.
diff --git a/include/common/buf.h b/include/common/buf.h
index a7bbb1f..1ad0052 100644
--- a/include/common/buf.h
+++ b/include/common/buf.h
@@ -484,15 +484,6 @@
 	return len;
 }
 
-/* b_putstr() : tries to copy string <str> into output data at buffer <b>.
- * Supports wrapping. Data are truncated if buffer is too short. It returns the
- * number of bytes copied.
- */
-static inline size_t b_putstr(struct buffer *b, const char *str)
-{
-	return b_putblk(b, str, strlen(str));
-}
-
 
 #endif /* _COMMON_BUF_H */