Cleanup: remove unused interfaces for helpers

I can only guess here: maybe they were added to more clearly document the public
interface of the classes? If so, I don't think that works. Developers who are
not familiar with the convention will just add a new public method to the class
without updating the interface.

pkg/gui/controllers/helpers/patch_building_helper.go

@@ -9,10 +9,6 @@ import (
 	"github.com/jesseduffield/lazygit/pkg/gui/types"
 )
 
-type IPatchBuildingHelper interface {
-	ValidateNormalWorkingTreeState() (bool, error)
-}
-
 type PatchBuildingHelper struct {
 	c *HelperCommon
 }