Remove CanUseFastAttribute subroutine from the generator

Remove CanUseFastAttribute subroutine from the generator as it makes the
code more complex but has no impact on the generated code.
Only SVG animated types cannot use getFastAttribute, however, no attribute
of SVG animated type is specified to [Reflect].

R=haraken@chromium.org

Review URL: https://codereview.chromium.org/19341003

git-svn-id: svn://svn.chromium.org/blink/trunk@154286 bbb929c8-8fbe-4397-9dbb-9b2b20218538