Remove the date modified otherwise we fail the Debian reproducibility test.

The reason for the failure is that those builds might run at a different date
from the upload, or the date on the system running it might be different from
the upload date, therefore we will generate different binaries and fail the
reproducibility test.

--- a/libntech/libutils/man.c
+++ b/libntech/libutils/man.c
@@ -69,7 +69,7 @@
         strftime(date_modified, 19, "%Y-%m-%d", &t);
     }
 
-    WriterWriteF(out, ".TH %s 8 \"%s\" \"CFEngine\" \"System Administration\"\n", program_upper, date_modified);
+    WriterWriteF(out, ".TH %s 8 \"CFEngine\" \"System Administration\"\n", program_upper);
 }
 
 static void WriteAvailability(Writer *out, const char *program)