deprecate iocshFindCommand()

This function, and struct iocshFuncDef, expose
internal details.  Specifically iocshCmdDef::func .
Which prevents changing/extending the iocsh function
signature.

Deprecate in favor of iocshCmd() and iocshRun().

modules/libcom/src/iocsh/iocsh.h

@@ -76,7 +76,7 @@ epicsShareFunc void epicsShareAPI iocshRegister(
 epicsShareFunc void epicsShareAPI iocshRegisterVariable (
     const iocshVarDef *piocshVarDef);
 epicsShareFunc const iocshCmdDef * epicsShareAPI iocshFindCommand(
-    const char* name);
+    const char* name) EPICS_DEPRECATED;
 epicsShareFunc const iocshVarDef * epicsShareAPI iocshFindVariable(
     const char* name);