Remove DOTNET_HOST_PATH workaround

[Youssef1313]

#6751 is adding a workaround to unblock our use of RC2.
Roslyn runs csc apphost which requires .NET 10 runtimes. If not globally installed, this currently fail. This is worked around by setting DOTNET_HOST_PATH, which will be read in https://github.com/dotnet/roslyn/blob/bb57f4643bb3d52eb7626f9863da177d9e219f1e/src/Compilers/Core/MSBuildTask/ManagedToolTask.cs#L244

[Youssef1313]

This is similar to dotnet/roslyn#80742