Land #6031, delete unused -a db_export option

lib/msf/ui/console/command_dispatcher/db.rb

@@ -1777,7 +1777,7 @@ class Db
       case arg
       when '-h','--help'
         print_line "Usage:"
-        print_line "    db_export -f <format> [-a] [filename]"
+        print_line "    db_export -f <format> [filename]"
         print_line "    Format can be one of: #{export_formats.join(", ")}"
       when '-f','--format'
         format = args.shift.to_s.downcase

spec/lib/msf/ui/console/command_dispatcher/db_spec.rb

@@ -321,7 +321,7 @@ describe Msf::Ui::Console::CommandDispatcher::Db do
         db.cmd_db_export "-h"
         @output.should =~ [
           "Usage:",
-          "    db_export -f <format> [-a] [filename]",
+          "    db_export -f <format> [filename]",
           "    Format can be one of: xml, pwdump"
         ]
       end