Include pkg/steep_icecavity by leveraging pkg/shelfice files #2908

Job	Run time
doc_latex	3m 25s
forward (offline_exf_seaice)	4m 26s
doc_html	1m 56s
openad (global_ocean.90x40x15)	9m 20s
forward (global_ocean.cs32x15)	3m 25s
forward (tutorial_deep_convection)	2m 38s
openad-other (global_oce_latlon)	10m 16s
forward (aim.5l_cs)	1m 45s
openad-other (halfpipe_streamice)	10m 45s
forward (isomip)	3m 1s
openad-other (hs94.1x64x5)	7m 18s
forward (global_ocean.90x40x15)	1m 53s
openad-other (isomip)	11m 4s
forward (tutorial_plume_on_slope)	1m 38s
openad-other (tutorial_global_oce_biogeo)	10m 0s
forward (tutorial_advection_in_gyre)	1m 15s
openad-other (tutorial_global_oce_optim)	7m 56s
forward (hs94.cs-32x32x5)	1m 42s
openad-other (tutorial_tracer_adjsens)	9m 5s
forward (tutorial_global_oce_biogeo)	1m 32s
forward (tutorial_global_oce_in_p)	1m 13s
forward (tutorial_cfc_offline)	1m 8s
	1h 46m 41s

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