D3D11: Add logic to disassociate EGL image storages. The TextureStorage classes for External and EGLImages were missing the logic to disassociate from images. This lead to the images continuing to hold references to deleted storages. Bug: chromium:1415330 Change-Id: I8303f6751d87a9b0a52993c7d4e9509b086b93f3 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4328347 Reviewed-by: Peng Huang <penghuang@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>