Fix unlink() error report in KeepFileRestoredFromArchive()

KeepFileRestoredFromArchive() has been using an incorrect WAL segment
name in the error report for an unlink() failure.

Even without 1200dfd60c, this was of consequence only on WIN32, where
we would miss to report a segment name suffixed by ".deleted%u".

Oversight in 60df192aea, for what looks like a copy-pasto to me.

Reported-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/CAHGQGwHSbJnUmWCuF-QNUsGYF=iSSuzLRx1z_dLfYFwfbTu4Cw@mail.gmail.com

src/backend/access/transam/xlogarchive.c

@@ -398,7 +398,7 @@ KeepFileRestoredFromArchive(const char *path, const char *xlogfname)
 			ereport(FATAL,
 					(errcode_for_file_access(),
 					 errmsg("could not remove file \"%s\": %m",
-							xlogfpath)));
+							oldpath)));
 #endif
 		reload = true;
 	}