Removes mesosize and cfize

[jasonheath]

Removes mesosize and cfize functionality and references where appropriate. For example, removes plan files and source explicitly relating to those but doesn't change text fixtures or changelogs.

There is a section of BUILDING.md that uses cloud foundry as an example that will need to be addressed but I didn't want to come up with an alternate example yet. Others should feel free to remove that section or rewrite it as they feel inclined.

Also, I probably missed something else but this is a pretty good scrubbing that is passing the verify pipeline and has the commands gone from the hab binary.

[admin@jah-wah | ~/Development/habitat/target/debug | jah/rm-mesos-and-cloud-foundry|u=]
$ ./hab pkg export
hab-pkg-export 2.0.16
Exports the package to the specified format

USAGE:
    hab pkg export <SUBCOMMAND>

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

SUBCOMMANDS:
    container    Container exporter
    help         Prints this message or the help of the given subcommand(s)
    tar          Tar exporter

@agadgil-progress: Added you as a reviewer because this probably interacts with your CLAP work a bit

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[mwrock]

This feels good to look at!

[jasonheath]

@mwrock: Made one last change if you can eyeball the BUILDING.md

@agadgil-progress: Planning on merging this Monday. I don't think this meaningfully impacts you but still highlighting it.

[mwrock]

Looks good. I don't see any issue with merging now.

[IanMadd]

Docs suggestions

[jasonheath]

Going ahead and merging per Matt's feedback and Ian's doc review.