refactor: remove Table from Relationship

Just having the QualifiedIdentifier gets us closer to having
Relationship as a Table attribute since it avoids a cyclic dependency

* remove unnecessary findTable
* modify RootSpec test

src/PostgREST/DbStructure/Table.hs

@@ -4,11 +4,10 @@
 module PostgREST.DbStructure.Table
   ( Column(..)
   , Table(..)
-  , tableQi
   , TablesMap
   ) where
 
-import qualified Data.Aeson as JSON
+import qualified Data.Aeson          as JSON
 import qualified Data.HashMap.Strict as M
 
 import PostgREST.DbStructure.Identifiers (FieldName,
@@ -34,9 +33,6 @@ data Table = Table
 instance Eq Table where
   Table{tableSchema=s1,tableName=n1} == Table{tableSchema=s2,tableName=n2} = s1 == s2 && n1 == n2
 
-tableQi :: Table -> QualifiedIdentifier
-tableQi Table{tableSchema=s, tableName=n} = QualifiedIdentifier s n
-
 data Column = Column
   { colTable       :: Table
   , colName        :: FieldName