Temporarily remove coveralls + fossa badges

The newly add GitHub workflow, which replaces Travis and Appveyor
does not support publishing coverage (coveralls) and license
(fossa) data yet (formerly done by Travis).

This commit removes the corresponding badges from README. It shall
be reverted once coveralls and fossa are re-enabled.

Signed-off-by: Lukas Puehringer <lukas.puehringer@nyu.edu>

README.md

@@ -1,9 +1,7 @@
 # <img src="https://cdn.rawgit.com/theupdateframework/artwork/3a649fa6/tuf-logo.svg" height="100" valign="middle" alt="TUF"/> A Framework for Securing Software Update Systems
 
 ![Build](https://github.com/theupdateframework/tuf/workflows/Run%20TUF%20tests%20and%20linter/badge.svg)
-[![Coveralls](https://coveralls.io/repos/theupdateframework/tuf/badge.svg?branch=develop)](https://coveralls.io/r/theupdateframework/tuf?branch=develop)
 ![Dependabot Status](https://api.dependabot.com/badges/status?host=github&repo=theupdateframework/tuf)
-[![FOSSA Status](https://app.fossa.com/api/projects/custom%2B162%2Fgithub.com%2Ftheupdateframework%2Ftuf.svg?type=shield)](https://app.fossa.com/projects/custom%2B162%2Fgithub.com%2Ftheupdateframework%2Ftuf?ref=badge_shield)
 [![CII](https://bestpractices.coreinfrastructure.org/projects/1351/badge)](https://bestpractices.coreinfrastructure.org/projects/1351)
 [![PyPI](https://img.shields.io/pypi/v/tuf)](https://pypi.org/project/tuf/)