Remove some unused mojo definitions.

Remove dead mojo definitions.

BUG=993189

Change-Id: I94d2ab50cf5314cf351a245f78f35b0769f105a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2630605Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843777}

content/common/native_types.mojom

@@ -8,9 +8,6 @@ module content.mojom;
 // ParamTraits for serialization. All of these should eventually be converted to
 // proper mojom definitions.
 
-[Native]
-struct FrameOwnerProperties;
-
 [Native]
 struct FrameReplicationState;
 
@@ -22,17 +19,11 @@ enum ScrollbarButtonsPlacement;
 [Native]
 enum ScrollerStyle;
 
-[Native]
-enum V8CacheOptions;
-
 // TODO(rockot): This should most likely be defined by network service mojom,
 // but the network service doesn't exist yet.
 [Native]
 enum NetworkConnectionType;
 
-[Native]
-struct WebCursor;
-
 [Native]
 struct SyntheticSmoothDrag;