[10.0.2xx] Remove IDE0370 NoWarn workaround

[mthalman]

A NoWarn was added for IDE0370: dotnet/dotnet#4085 (review) as a workaround to handle differences in the SDK used between a stage 1 and stage 2 build. This can be removed after the next rebootstrap of the VMR (when it will be updated to reference a newer SDK version); it's current using 11.0.100-alpha.1.25618.104. As part of that, the unnecessary null-forgiving operators should be removed as well.

[mthalman]

After dotnet/dotnet#4224 is merged, this work can proceed

[Frulfump]

After dotnet/dotnet#4224 is merged, this work can proceed

Merged now!

[mthalman]

My bad. This change was specific to 10.0.2xx. So dotnet/dotnet#4224 is not relevant here.

That means this won't be ready until after the February release.