Revert "Replace style sharing cousin list search with LRU"

This reverts commit r156070 because of a performance regression.

BUG=273605
TBR=esprehn

Review URL: https://chromiumcodereview.appspot.com/22966004

git-svn-id: svn://svn.chromium.org/blink/trunk@156247 bbb929c8-8fbe-4397-9dbb-9b2b20218538