init: Remove --lm_overview_gradient_image from WM command line.
init: Remove --lm_overview_gradient_image from WM command line.

This should've happened in 6babb283d7a0798b9dba4708fab5c030e4f1e691,
which removed the flag.

But the previous change appears to be broken to me even after this
fix -- unmagnified windows aren't getting dimmed in overview mode for
me.

BUG=none
TEST=tried it

Review URL: http://codereview.chromium.org/1123002

joshfire/chromiumos-platform-init