otautil: Clean up obsolete includes.

external/zlib and external/safe-iop/include were used by Zip.c, which
became obsolete after [1].

Removing
 - <assert.h>: we no longer call assert(3);
 - <limits.h>: we no longer use PATH_MAX;
 - <stdio.h>: we don't need FILE anymore;
 - <stdlib.h>: no more malloc(3)/calloc(3);
 - <unistd.h>: was once needed for lseek(2);
 - <string.h>: no more memset(3).

Adding
 - <stdint.h> for SIZE_MAX.

[1] commit 8cf5c8f60f51049278b08ae4cbc31df397b651fd: "Replace minzip
with libziparchive".

Test: `mmma bootable/recovery`
Change-Id: I349e909ba83d0f6ade5f92856ce3934f29fdca6c
diff --git a/otautil/SysUtil.cpp b/otautil/SysUtil.cpp
index a8d5f4a..a2133b9 100644
--- a/otautil/SysUtil.cpp
+++ b/otautil/SysUtil.cpp
@@ -16,17 +16,12 @@
 
 #include "SysUtil.h"
 
-#include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
-#include <limits.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
+#include <stdint.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <sys/types.h>
-#include <unistd.h>
 
 #include <algorithm>
 #include <string>