Removing L from data table

[tawheeler]

I am removing L from the initial table because altitude layer can be inferred from airplane altitude in the state traces. The docs need to be updated to reflect this.

[smostars]

I updated 4 files in the "03_TrackPlotting" folder to address the above change: AA120Q.jl, README.md, Solution.ipynb, and Assignment.ipynb