Removed duplicated virtual computePreferredLogicalWidths()

RenderDeprecatedFlexibleBox, RenderMenuList and RenderSlider does not
need this duplicated code from RenderBlock.
Now code will go through the updateFirstLetter() check but first letter
is disabled for RenderDeprecatedFlexibleBox, RenderMenuList.

This patch removes the overridden function.

BUG=263225

Review URL: https://codereview.chromium.org/602353002

git-svn-id: svn://svn.chromium.org/blink/trunk@183174 bbb929c8-8fbe-4397-9dbb-9b2b20218538