Remove Landscape badge until Landscape fixed

Pillow isn't at 100% code health, there's plenty of PEP8 and Pyflakes warnings in our Travis CI. This is a bug in Landscape: 

https://github.com/landscapeio/landscape-issues/issues/70

Let's remove the badge until Landscape's working properly.

Re: #895.
Mention Coveralls

[CI skip]
Merge branch 'master' of https://github.com/python-pillow/Pillow