Remove more unexported or exported but unused resources

missingImage.png and textAreaResizeCorner.png are both unreferenced in Blink
(though interesting Blink does reference copies of those images that live
in the Chromium tree).

For the images I'm removing (and removing their lines from blink_resources.grd),
I've checked on the Chromium side that these images are unused (git blame suggests
that they used to be references but were removed at some point).

R=abarth

Review URL: https://codereview.chromium.org/25653007

git-svn-id: svn://svn.chromium.org/blink/trunk@158823 bbb929c8-8fbe-4397-9dbb-9b2b20218538