Remove AC_HEADER_TIME

Autoconf 2.59d (released in 2006) [1] started promoting several macros
as not relevant for newer systems anymore, including the `AC_HEADER_TIME`.

This macro checks if both `<sys/time.h>` and `<time.h>` can be included
at the same time and defines the `TIME_WITH_SYS_TIME` and
`HAVE_SYS_TIME_H` symbols. On current system such check is not relevant
anymore because in case both headers are present both can be also
included at the same time.

This patch simplifies this checking.

Refs:
[1] http://git.savannah.gnu.org/cgit/autoconf.git/tree/NEWS
[2] https://www.gnu.org/software/autoconf/manual/autoconf-2.69/autoconf.html

Author: petk

ext/mbstring/config.m4

@@ -98,7 +98,6 @@ int main() { return foo(10, "", 3.14); }
       AC_CHECK_SIZEOF(int, 4)
       AC_CHECK_SIZEOF(short, 2)
       AC_CHECK_SIZEOF(long, 4)
-      AC_HEADER_TIME
       AC_FUNC_ALLOCA
       AC_FUNC_MEMCMP
       AC_CHECK_HEADER([stdarg.h], [

ext/xmlrpc/libxmlrpc/acinclude.m4

@@ -24,7 +24,6 @@ AC_CHECK_SIZEOF(int, 4)
 AC_CHECK_SIZEOF(long, 4)
 AC_CHECK_SIZEOF(long long, 8)
 AC_TYPE_SIZE_T
-AC_HEADER_TIME
 AC_TYPE_UID_T