Revert "Go back to cleaning up MIP levels on texture export rather than assuming dirty"

This reverts commit 01d6fc9d8415e400a7eac95518356ecf341aa5cb.

Reason for revert: layout tests.

Original change's description:
> Go back to cleaning up MIP levels on texture export rather than assuming dirty
> on texture import.
> 
> Bug: skia:8155
> Change-Id: I23399f442d52c73906829132f798eda260b6d4ae
> Reviewed-on: https://skia-review.googlesource.com/143291
> Auto-Submit: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>
> Reviewed-by: Brian Osman <brianosman@google.com>

TBR=bsalomon@google.com,brianosman@google.com

Change-Id: Ice4cb4e253e52d67eb8bd6e2a12ccc844b7bfa8d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:8155
Reviewed-on: https://skia-review.googlesource.com/143380
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed