func (e removeCallableInput) Apply(ast *syntax.Ast) (int, error) {
	count := 0
	for _, target := range ast.Callables.List {
		if target.GetId() == e.Callable.GetId() &&
			target.File().FullPath == e.Callable.File().FullPath {
			e.remove(target.GetInParams())
			count++
		}
	}
	return count, nil
}
Apply removes an input parameter from a callable in the given AST object.

The first return value indicates the number places where a change was
made.

The AST is not required to have been compiled.
package refactoring
import (
	"fmt"
	"os"
	"github.com/martian-lang/martian/martian/syntax"
)
type removeCallableInput struct {
	Callable syntax.Callable
	Param    string
}