AIO_runtime_apihost should not be present in .env

[MichaelGoberling]

AIO_runtime_apihost should be removed from the .env files generated by aio app use and aio app init.

Environment variables should be reserved for non-default values.

Note: The reason this variable cannot currently be removed is because wskdebug uses it to get openwhisk server runtime docker image data. We will need to find a way to get wskdebug this value without including it as part of .env.