Remove unused operation names (#503)

These are not standalone operations anymore, they are part of the
`alter_column` operation.

pkg/migrations/op_common.go

@@ -26,15 +26,6 @@ const (
 	OpNameDropMultiColumnConstraint OpName = "drop_multicolumn_constraint"
 	OpRawSQLName                    OpName = "sql"
 	OpCreateConstraintName          OpName = "create_constraint"
-
-	// Internal operation types used by `alter_column`
-
-	OpNameRenameColumn       OpName = "rename_column"
-	OpNameSetUnique          OpName = "set_unique"
-	OpNameSetNotNull         OpName = "set_not_null"
-	OpNameSetForeignKey      OpName = "set_foreign_key"
-	OpNameSetCheckConstraint OpName = "set_check_constraint"
-	OpNameChangeType         OpName = "change_type"
 )
 
 const temporaryPrefix = "_pgroll_new_"
@@ -121,9 +112,6 @@ func (v *Operations) UnmarshalJSON(data []byte) error {
 		case OpNameDropIndex:
 			item = &OpDropIndex{}
 
-		case OpNameSetUnique:
-			item = &OpSetUnique{}
-
 		case OpRawSQLName:
 			item = &OpRawSQL{}
 
@@ -213,9 +201,6 @@ func OperationName(op Operation) OpName {
 	case *OpDropIndex:
 		return OpNameDropIndex
 
-	case *OpSetUnique:
-		return OpNameSetUnique
-
 	case *OpRawSQL:
 		return OpRawSQLName