Remove unused 'important_board_members' column from schema #751

Job	Run time
Test Collections Publisher / Run RSpec	1m 51s
Test Collections / Run RSpec	1m 42s
Test Contacts Admin / Run RSpec	1m 56s
Test Content Data API / Run RSpec	3m 26s
Test Content Publisher / Run RSpec	3m 20s
Test Content Store / Run RSpec	32s
Test Content Tagger / Run RSpec	2m 19s
Test Email Alert Frontend / Run RSpec	1m 5s
Test Email Alert Service / Run RSpec	34s
Test Feedback / Run RSpec	1m 28s
Test Finder Frontend / Run RSpec	1m 32s
Test Frontend / Run RSpec	3m 42s
Test Government Frontend / Run Minitest	5m 13s
Test HMRC Manuals API / Run RSpec	29s
	29m 9s

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