FIX: Remove NotImplementedException when loading outdated binding overrides from json (#1626)

* FIX: Remove NotImplementedException when loading outdated binding overrides from json

* update ticket number in changelog after moving to ISXB project

Author: jamesmcgill

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -24,6 +24,7 @@ however, it has to be formatted properly to pass verification tests.
 - Fixed Switch Pro, DualShock 4, DualSense gamepads becoming current on PC/macOS when no controls are changing ([case ISXB-223](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-223))).
 - Fixed an issue that made OnScreenStick unusable when used in conjunction with PlayerInput in Auto-Switch devices mode, or with any code that changes user/device pairing on unsued device activity being detected ([case ISXB-48](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-48)).
 - Fixed issue where input events were being suppressed during interactive action rebinding even when when their controls were excluded ([case ISXB-367](https://issuetracker.unity3d.com/issues/mouse-position-and-mouse-click-input-not-recognized-when-rebinding-is-active)).
+- Display a warning instead of throwing a NotImplementedException when loading binding overrides from json when some of the entries have become outdated ([case ISXB-375](https://issuetracker.unity3d.com/product/unity/issues/guid/ISXB-375)).
 
 ### Actions
 - Extended input action code generator (`InputActionCodeGenerator.cs`) to support optional registration and unregistration of callbacks for multiple callback instances via `AddCallbacks(...)` and `RemoveCallbacks(...)` part of the generated code. Contribution by [Ramobo](https://github.com/Ramobo) in [#889](https://github.com/Unity-Technologies/InputSystem/pull/889).

Packages/com.unity.inputsystem/InputSystem/Actions/InputActionRebindingExtensions.cs

@@ -1272,7 +1272,7 @@ private static void LoadBindingOverridesFromJsonInternal(this IInputActionCollec
                     }
                 }
 
-                throw new NotImplementedException();
+                Debug.LogWarning("Could not override binding as no existing binding was found with the id: " + entry.id);
             }
         }