tools: delete -p in ndnsec-export/import help

ndnsec-export and ndnsec-import man pages are also updated.

refs #4313

Change-Id: I1ba41123c5fb46f2e408da3d55dfe9bef56d5b27
diff --git a/tools/ndnsec/import.cpp b/tools/ndnsec/import.cpp
index 4137324..a818a3a 100644
--- a/tools/ndnsec/import.cpp
+++ b/tools/ndnsec/import.cpp
@@ -33,7 +33,7 @@
   std::string input("-");
   std::string importPassword;
 
-  po::options_description description("General Usage\n  ndnsec import [-h] [-p] input \nGeneral options");
+  po::options_description description("General Usage\n  ndnsec import [-h] input \nGeneral options");
   description.add_options()
     ("help,h", "produce help message")
     ("input,i", po::value<std::string>(&input), "input source, stdin if -")