Remove unneeded setNeedsLayouts from RenderTableSection

As best I can tell, these setNeedsLayouts don't accomplish anything.
Elliott and I dug through the changes that added them. The tests
added with those patches pass without the setNeedsLayouts. We tried
for a while to come up with a test case the setNeedsLayouts were
needed and couldn't.

The cellChildrenFlex part is needed though so that we only call
setOverrideLogicalContentHeightFromRowHeight in the right cases.

Review URL: https://chromiumcodereview.appspot.com/21975003

git-svn-id: svn://svn.chromium.org/blink/trunk@155951 bbb929c8-8fbe-4397-9dbb-9b2b20218538