Drop `bootstrap_form`

[benmelz]

bootstrap_form isn't really a necessary library for us to depend on. We just style with bootstrap directly everywhere else.

[werebus]

I guess. But, in my opinion, the forms on this site look pretty good (I particularly like the in-form validation errors). And man, this haml looks nice and clean:

st-pax/app/views/users/_form.html.haml

Lines 3 to 10 in b503422

	= bootstrap_form_with model: @user, local: true do |f|
	= f.text_field :name
	= f.text_field :spire, placeholder: '12345678@umass.edu'
	= f.form_group do
	= f.check_box :active
	=f.form_group do
	= f.check_box :admin
	= f.primary 'Save'