remove manifests.output field from schema

[ericzzzzzzz]

• manifests.output field was introduced for users to specify kpt hydration output dir, but this the logic behind of it is never implemented.
• Specifying this filed in multiple modules project can lead to render output in different places, which are hard to manage, also there is chance that this filed in different sub-modules may override each other.
• Also, having this field for a dedicated render kpt creates more confusion.
• As the reasons above, let's remove the field from schema.

[ericzzzzzzz]

skaffold/pkg/skaffold/schema/latest/config.go

Lines 687 to 689 in 23c5c16

	// Output is the path to the hydrated directory.
	Output string `yaml:"output,omitempty"`

this is the node we want to remove. Here is a guide for schema change https://github.com/GoogleContainerTools/skaffold/blob/main/DEVELOPMENT.md#making-a-config-change