Remove starboard dep on cobalt/build/contents_dir.gni (#4125) #9452

Job	Run time
linux-coverage / initialize	45s
linux-coverage / docker-build-image	1m 44s
linux-coverage / docker-unittest-image	46s
linux-coverage / linux_devel	14m 14s
linux-coverage / linux_debug	9m 9s
linux-coverage / linux_qa	7m 19s
linux-coverage / linux_gold	8m 30s
linux-coverage / linux_coverage_test	1h 7m 14s
linux-coverage / ${{ matrix.name }}_on_device_${{ matrix.shard }}	0s
	1h 49m 41s

Provide feedback