Revert of Enable a srcset 0x descriptor (https://codereview.chromium.org/305643006/)

Reason for revert:
This patch closed the tree with a '"update" on "Win7 Tests"' message. Reverting

Original issue's description:
> Enable a srcset 0x descriptor
> 
> According to recent spec changes, a "0x" descriptor should be correctly parsed,
> and imply intrinsic dimensions of infinity to the image.
> This CL enables that, and tests that intrinsic dimensions are impacted accordingly.
> 
> BUG=378252
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175196

TBR=eseidel@chromium.org,pdr@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=378252

Review URL: https://codereview.chromium.org/302083009

git-svn-id: svn://svn.chromium.org/blink/trunk@175197 bbb929c8-8fbe-4397-9dbb-9b2b20218538