Remove updateFirstLetter and firstLineBlock from RenderSVGText.

These two methods were originally added in
http://src.chromium.org/viewvc/blink?revision=61050&view=revision with an
associated crash test. The test (svg/text/text-style-invalid.svg) no longer
crashes with these two methods removed.

BUG=391288

Review URL: https://codereview.chromium.org/364223002

git-svn-id: svn://svn.chromium.org/blink/trunk@178057 bbb929c8-8fbe-4397-9dbb-9b2b20218538