Reland "Reland "Removes ui/platform_window/mojo as it is not used by anyone.""

This is a reland of 6700540dcbab00b4120fa39b41ea51d4c5fc3a3b
The Windows Dbg bot failure should have been fixed by the cl:
http://crrev.com/c/1635772.

Original change's description:
> Reland "Removes ui/platform_window/mojo as it is not used by anyone."
>
> This is a reland of 6eb61402c1b1b4301762c6aaaea28b2921cbf4c2
>
> Original change's description:
> > Removes ui/platform_window/mojo as it is not used by anyone.
> >
> > This is to remove the ref to some types under ui/base/ime/mojo, which will be removed later.
> >
> > Bug: 965908
> > Change-Id: I7979524066104c829b4f4e287a0ab87c9365f124
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1626055
> > Reviewed-by: Dominick Ng <dominickn@chromium.org>
> > Reviewed-by: Scott Violet <sky@chromium.org>
> > Commit-Queue: Shu Chen <shuchen@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#662924}
>
> Bug: 965908
> Change-Id: I6bb1c6d081ce235c959cc30e53d20b57dd0e1459
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1626841
> Reviewed-by: Dominick Ng <dominickn@chromium.org>
> Reviewed-by: Scott Violet <sky@chromium.org>
> Commit-Queue: Shu Chen <shuchen@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#663381}

Bug: 965908
Change-Id: Ibfed1d3a64c45c5ba64bbd5f97313f5decc50bc0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1630787
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665569}
12 files changed