Remove updateFirstLetter and firstLineBlock from RenderTable.

These methods were added when first letter support was initially added in
https://src.chromium.org/viewvc/blink?revision=5249&view=revision. Removing
them causes no test failures, but there does not appear to be any tests that
where added initially.

BUG=391288

Review URL: https://codereview.chromium.org/370593002

git-svn-id: svn://svn.chromium.org/blink/trunk@178077 bbb929c8-8fbe-4397-9dbb-9b2b20218538