Clean up computePreferredLogicalWidths functions in TableLayout subclasses
https://bugs.webkit.org/show_bug.cgi?id=110515

Reviewed by Tony Chang.

No change in behavior. This is just a cleanup in preparation for other
refactoring to this code.

* rendering/FixedTableLayout.cpp:
(WebCore::FixedTableLayout::calcWidthArray):
Move a FIXME here from computePreferredLogicalWidths. It makes more sense here.
(WebCore::FixedTableLayout::computePreferredLogicalWidths):
-Remove outdated or unhelpful comments.
-Isolate the fixed width codepath to make it a bit less convoluted.
(WebCore::FixedTableLayout::layout):
* rendering/FixedTableLayout.h:
The argument to calcWidthArray is never used. Remove it.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143683 268f45cc-cd09-0410-ab3c-d52691b4dbfc