change collection params in calculate_indices to reflect that C3 is default landsat collection now

[Kooie-cate]

calculate_indices in https://github.com/GeoscienceAustralia/dea-notebooks/blob/develop/Tools/dea_tools/bandindices.py was written before collection 3. the need to specify which Landsat collection is in use causes problems for this tool's use in Land Cover. making changes to the tool so that if passed 'ga_ls' it assumes ga_ls_c3 as the default Landsat collection would solve this problem.

changes also need to be made to the frequently used code notebook where this' tool's use is demonstrated.