remove unused includes

This patch removes includes that are not used. The removals were found with
include-what-you-use which checks if any of the symbols from a header is
in use.

src/boot/bootctl.c

@@ -41,7 +41,6 @@
 #include "efivars.h"
 #include "build.h"
 #include "util.h"
-#include "utf8.h"
 
 static int verify_esp(const char *p, uint32_t *part, uint64_t *pstart, uint64_t *psize, sd_id128_t *uuid) {
         struct statfs sfs;