Revert "Add SkImageInfoValidConversion() and SkImageInfoIsValid"

Revert "Add SkImageInfoValidConversion() and SkImageInfoIsValid"

This reverts commit cf5d6caff7a58f1c7ecc36d9a91ccdada5fc7b78.

Reason for revert: Chrome DEPS roll failing, based on the unit tests, I suspect this is the cause.

Original change's description:
> Add SkImageInfoValidConversion() and SkImageInfoIsValid
>
> The idea is share these standards for the following:
> SkImage::readPixels()
> SkCanvas::readPixels()
> SkCanvas::writePixels()
> SkBitmap::readPixels()
> SkPixmap::readPixels()
>
> On the raster side, SkPixmap::readPixels() is the right
> place to check, because all raster calls go through
> there eventually.  Then at lower levels (ex: SkPixelInfo),
> we can assert.
>
> There's not really a unifying location for gpu calls,
> so I've added this in multiple places.  I haven't really
> dug into the gpu code to SkASSERT() on invalid cases
> that we will have already caught.
>
> Follow-up work:
> Similar refactor for SkReadPixelRec::trim().
> Code cleanup in SkPixelInfo::CopyPixels()
>
> BUG=skia:6021
>
> Change-Id: I91ecce10e46c1a6530f0af24a9eb8226dbecaaa2
> Reviewed-on: https://skia-review.googlesource.com/6887
> Reviewed-by: Brian Osman <brianosman@google.com>
> Reviewed-by: Mike Reed <reed@google.com>
>

TBR=mtklein@google.com,msarett@google.com,brianosman@google.com,reed@google.com,reviews@skia.org
# Not skipping CQ checks because original CL landed > 1 day ago.
BUG=skia:6021

Change-Id: I63b88e90bdbb3051a14de00ac73a8351ab776d25
Reviewed-on: https://skia-review.googlesource.com/7095
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>