Change guard for remove foreign key spec
Change guard for remove foreign key spec

After change to use drop_foreign_key, this should theoretically
work on any adapter that supports foreign_key parsing, so use that
as the guard.

t-morgan/sequel,yazshel/sequel,t-morgan/sequel,uhoh-itsmaciek/sequel,Marketcircle/sequel,beni55/sequel,beni55/sequel,offshore-safety/sequel,gferguson-gd/sequel,seeARMS/sequel,freshpay/sequel,nju520/sequel,freshpay/sequel,pfarrell/sequel,uhoh-itsmaciek/sequel,reubano/sequel,dennis-d/custom_sequel,nicohvi/sequel,gferguson-gd/sequel,mpalmer/sequel,davidbegin/sequel,offshore-safety/sequel,pfarrell/sequel,knut2/sequel,offshore-safety/sequel,knut2/sequel,nju520/sequel,dennis-d/custom_sequel,yazshel/sequel,chef/sequel,davidbegin/sequel,seeARMS/sequel,mpalmer/sequel,nicohvi/sequel,reubano/sequel