Explicit dynamic conversion is redundant

We have
- An [implicit dynamic conversion](https://github.com/dotnet/csharplang/blob/master/spec/conversions.md#implicit-dynamic-conversions) from an expression of type `dynamic` to any type T.
- All of the implicit conversions are also [explicit conversions](https://github.com/dotnet/csharplang/blob/master/spec/conversions.md#explicit-conversions).
- An [explicit dynamic conversion](https://github.com/dotnet/csharplang/blob/master/spec/conversions.md#explicit-dynamic-conversions) from an expression of type `dynamic` to any type T.

This list is redundant, as it includes the conversion "from an expression of type `dynamic` to any type T" twice. I suspect the explicit dynamic conversion is supposed to be a conversion from type rather than a conversion from expression.