Add @Deprecated tag to Toast.getView()

For some reason I had added @deprecated inside javadocs but forgot to
add @Deprecated to the method on ag/10117117. Repo-hooks only
warned me now that touched that method for something unrelated.
Curiously even api/current.txt in that CL has the method marked as
@Deprecated.

Bug: 128611929
Bug: 144754526
Test: Builds
Change-Id: I8e4a58ae5ba2204aaced6d7a83746b17573a8c97