Removes cmake_ext_mod (files moved to cmake) (#2041)

At one time this content was a git submodule shared between several
projects but that time has long passed.

config/cmake/GetTimeOfDayTest.cpp

@@ -0,0 +1,26 @@
+/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
+ * Copyright by The HDF Group.                                               *
+ * All rights reserved.                                                      *
+ *                                                                           *
+ * This file is part of HDF5.  The full HDF5 copyright notice, including     *
+ * terms governing use, modification, and redistribution, is contained in    *
+ * the COPYING file, which can be found at the root of the source code       *
+ * distribution tree, or in https://www.hdfgroup.org/licenses.               *
+ * If you do not have access to either file, you may request a copy from     *
+ * help@hdfgroup.org.                                                        *
+ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
+#if defined (TRY_SYS_TIME_H)
+#include <sys/time.h>
+/* #include <time.h> */
+#endif
+
+
+#if defined (TRY_TIME_H)
+#include <time.h>
+#endif
+
+int main(int argc, char **argv) {
+	  struct timeval t1;
+	  gettimeofday(&t1, 0x00);
+	return 0;
+}