Do not print shortcut_function names with available_layers()

[stephhazlitt]

Return for bcmaps::available_layers() is a list of map layer names and titles and then a list of shortcut_function() names—which are the same as the map layer name. Remove return of shortcut names and update documention.

[ateucher]

I remember now why I had that - in case we added a layer to bcmaps.rdata and we hadn't updated bcmaps on CRAN yet, there would be a layer that you could get via get_layer("new_layer") but new_layer() wouldn't work (until we updated bcmaps with the new shortcut function.
But I agree it's still confusing. What about keeping the shortcut_function column but make it TRUE/FALSE to indicate that the shortcut function exists (or not)?

> available_layers()
                 Item                                              Title shortcut_function
1            airzones                         British Columbia Air Zones              TRUE
2            bc_bound                                        BC Boundary              TRUE
3       bc_bound_hres                      BC Boundary - High Resolution              TRUE
4        ecoprovinces                      British Columbia Ecoprovinces              TRUE
5          ecoregions                        British Columbia Ecoregions              TRUE
6         ecosections                       British Columbia Ecosections              TRUE
7         gw_aquifers British Columbia's developed ground water aquifers              TRUE
8          hydrozones     Hydrologic Zone Boundaries of British Columbia              TRUE
9      municipalities                    British Columbia Municipalities              TRUE
10           nr_areas       British Columbia Natural Resource (NR) Areas              TRUE
11       nr_districts   British Columbia Natural Resource (NR) Districts              TRUE
12         nr_regions     British Columbia Natural Resource (NR) Regions              TRUE
13 regional_districts                British Columbia Regional Districts              TRUE
14    water_districts      British Columbia's Water Management Districts              TRUE
15    water_precincts      British Columbia's Water Management Precincts              TRUE
16   watercourses_15M       British Columbia watercourses at 1:15M scale              TRUE
17    watercourses_5M        British Columbia watercourses at 1:5M scale              TRUE
18      wsc_drainages      Water Survey of Canada Sub-Sub-Drainage Areas              TRUE

[stephhazlitt]

Perfect, and a good reason for having it there.