Stop special casing runnable root commands
Stop special casing runnable root commands

The special case code to handle a runnable root command had some
problems.  It was noticed that if you created a runnable root and a
subcommand.  And the subcommand was then executed with both a valid and
invalid flag, the error message was about the valid flag being invalid.
For example

./command subcommand --goodflag=10 --badflag=10

Would fail and tell you that --goodflag was an invalid flag. Instead if
we just do away with the special Command.execute() for the root command
the parser for subcommand is what prints the error and it gets it
right...

vikstrous/cobra,abhishekgahlot/cobra,jlowdermilk/cobra,k4rtik/cobra,sdomino/cobra,jrossi/cobra,nicrioux/cobra,spf13/cobra,anthonyfok/cobra,gosuri/cobra,simlelievre/cobra,liggitt/cobra,eparis/cobra,akutz/cobra