goose: use marker functions instead of comments

To avoid making this CL too large, I did not migrate the existing goose
comments through the repository.  This will be addressed in a subsequent
CL.

Reviewed-by: Tuo Shan <shantuo@google.com>

internal/goose/testdata/InterfaceBindingReuse/foo/foo.go

@@ -28,8 +28,6 @@ func (b *Bar) Foo() string {
 	return string(*b)
 }
 
-//goose:provide
-//goose:bind provideBar Fooer *Bar
 func provideBar() *Bar {
 	mu.Lock()
 	provideBarCalls++
@@ -44,7 +42,6 @@ var (
 	provideBarCalls int
 )
 
-//goose:provide
 func provideFooBar(fooer Fooer, bar *Bar) FooBar {
 	return FooBar{fooer, bar}
 }