Clean up tests

[cknitt]

• Convert tests in .re syntax to .res
• Convert tests in .ml syntax to .res
• The build tests contain some example projects like bucklescript-tea or a very old version of ReasonReact. Are these still relevant? Can they be removed or replaced with different examples?

[cristianoc]

This an others? Likely to be revived soon?
Otherwise we can move to v12.

[cristianoc]

Already converted normal tests. There are only build tests to convert now -- which are not that many in comparison.