Convert modules/ca to use LIBCA_API instead of epicsShare

Also unified the header exclusion guard names,
removed a couple of files that are no longer used,
dropped the '3.13.7' from the Copyright header.

modules/ca/src/client/ca_client_context.cpp

@@ -34,7 +34,6 @@
 #include "errlog.h"
 #include "locationException.h"
 
-#define epicsExportSharedSymbols
 #include "iocinf.h"
 #include "oldAccess.h"
 #include "cac.h"