Assume that we have utime() and <utime.h>.

These are required by POSIX since SUSv2, and no live platforms fail
to provide them.  On Windows, utime() exists and we bring our own
<utime.h>, so we're good there too.  So remove the configure probes
and ad-hoc substitute code.  We don't need to check for utimes()
anymore either, since that was only used as a substitute.

In passing, make the Windows build include <sys/utime.h> only where
we need it, not everywhere.

This is part of a series of commits to get rid of no-longer-relevant
configure checks and dead src/port/ code.  I'm committing them separately
to make it easier to back out individual changes if they prove less
portable than I expect.

Discussion: https://postgr.es/m/15379.1582221614@sss.pgh.pa.us

src/include/port/win32_port.h

@@ -50,7 +50,6 @@
 #include <process.h>
 #include <signal.h>
 #include <direct.h>
-#include <sys/utime.h>			/* for non-unicode version */
 #undef near
 #include <sys/stat.h>			/* needed before sys/stat hacking below */