Remove workaround for facade reference

**.NET Core Version:**
.NET Core 5.0 (master branch)

**Have you experienced this same bug with .NET Framework?:**
No (not applicable)

**Problem description:**
For resolution of issue #2413 (PR #3098) a workaround for dotnet/sdk#3254 is required, this issue serves for tracking removal of the workaround once the SDK bug is resolved.

The bug affects all ProjectReference in that the generated deps.json doesn't contain the referenced version number, but currently only for System.Drawing it is causing problems for assembly resolution, so the workaround is only present there. Might be added to other references as required.

**Expected behavior:**
No workaround required for `ProjectReference` to a facade assembly

**Minimal repro:**
Reference a facade assembly and observe that the deps.json produced as build output does not include the version of the assembly you referenced:

```json
"runtime": {
"System.Drawing.dll": {}
}
```