Clean up truncated grid constructor with next ClimaCore release

[ilopezgp]

PR #1238 introduces an adjusted truncated mesh to substitute the previous implementation we had.

However, there is no need to do this in TC.jl or use TC.Grid objects in the process. The ClimaCore PR 812 implements the same truncated grid as PR #1238 as an internal ClimaCore function that does not use Grids, and requires one less Mesh to be constructed.

Once the dependency of TC on ClimaCore is updated to include the new formulation, the truncated grid in TC should be deleted in favor of the CC one.