Remove unnecessary broadcast type

[charleskawczynski]

It looks like we have two stencil styles, that from what I can tell have no reason to be different: a StencilStyle and a ColumnStencilStyle. For some reason, StencilStyle is used in result_style in broadcasted, and ColumnStencilStyle is used elsewhere.

I ran into an issue:

ERROR: LoadError: conflicting broadcast rules defined
  Broadcast.BroadcastStyle(::ClimaCore.Operators.StencilStyle, ::ClimaCore.Operators.ColumnStencilStyle) = ClimaCore.Operators.StencilStyle()
  Broadcast.BroadcastStyle(::ClimaCore.Operators.ColumnStencilStyle, ::ClimaCore.Operators.StencilStyle) = ClimaCore.Operators.ColumnStencilStyle()
One of these should be undefined (and thus return Broadcast.Unknown).
Stacktrace:
  [1] error(s::String)
    @ Base ./error.jl:35
  [2] 
    @ Base.Broadcast ./broadcast.jl:474
  [3] result_style(s1::ClimaCore.Operators.StencilStyle, s2::ClimaCore.Operators.ColumnStencilStyle)
    @ Base.Broadcast ./broadcast.jl:457
  [4] broadcasted(op::ClimaCore.Operators.GradientC2F{…}, args::Base.Broadcast.Broadcasted{…})
    @ ClimaCore.Operators ~/.julia/packages/ClimaCore/7GN1g/src/Operators/finitedifference.jl:3960

in a development branch. I think this change fixes this issue.

It looks like these were introduced in these two commits (from a while ago)

• d206152
• 7645f97

[charleskawczynski]

I have one more piece to add to this:

Base.Broadcast.result_style(x::Operators.ColumnStencilStyle, y::CUDAColumnStencilStyle) = y
Base.Broadcast.BroadcastStyle(
    x::Operators.ColumnStencilStyle,
    y::CUDAColumnStencilStyle,
) = y

in the cuda ext.