sources: remove dump files on start

When chronyd is starting, after the point where dump files are loaded,
remove all files in the dump directory that match the naming scheme used
for dump files. This prevents loading stale dump files that were not
saved in the latest run of chronyd.

main.c

@@ -158,6 +158,7 @@ ntp_source_resolving_end(void)
     SRC_ReloadSources();
   }
 
+  SRC_RemoveDumpFiles();
   RTC_StartMeasurements();
   RCL_StartRefclocks();
   NSR_StartSources();