[flow] Pass None to exact_reason param of mk_object_type to sto…

…p `ExactT` construction (1/n)

Summary:
I want to kill `ExactT`. To achieve that, we need to first migrate away all the sites that construct `ExactT`. One source of construction is in `slice_utils` [here](https://github.com/facebook/flow/blob/d9d9319cde578cff73e83071a4e62d992ceb855f/src/typing/slice_utils.ml#L50-L63), when we pass in a `Some _` for `exact_reason`.

In this series of diff, we will start the call sites where `def_reason` and `exact_reason` are the same, which should have no user visible changes. Therefore, we can stop the construction of `ExactT` in these instances by passing `None` instead.

In this diff, we migrate the callsite in `object_kit`

Changelog: [internal]

Reviewed By: panagosg7

Differential Revision: D56440367

fbshipit-source-id: ce712cea4c0e78569379ab0c92517b2ef63a1fdf

src/typing/object_kit.ml

@@ -489,7 +489,7 @@ module Kit (Flow : Flow_common.S) : OBJECT = struct
           let proto = ObjProtoT reason in
           Slice_utils.mk_object_type
             ~def_reason:reason
-            ~exact_reason:(Some reason)
+            ~exact_reason:None
             ~invalidate_aliases:false
             ~interface:None
             ~reachable_targs