Remove http partial image load tests from TestExpectations

These tests consistently pass (see bug), and the bug assigned
to them was closed long ago.

TBR=dpranke@chromium.org
BUG=237270
NOTRY=true

Review URL: https://codereview.chromium.org/716483002

git-svn-id: svn://svn.chromium.org/blink/trunk@185020 bbb929c8-8fbe-4397-9dbb-9b2b20218538