Revert "[mono] Roslyn does not support signing assemblies on non-windows" (#67)
Revert "[mono] Roslyn does not support signing assemblies on non-windows" (#67)

This reverts commit 665f843ac664eb2b4541242c1d6e364a9a838ac8.

Roslyn supports signing on !windows now, with 2.7+ . And this is bundled
with mono/master which uses roslyn 2.7+ .

Fixes https://github.com/mono/mono/issues/8495 .
mono/msbuild,mono/msbuild,mono/msbuild,mono/msbuild