A class's name is its constructor's name, so there's no need to treat it separately,
either in the parser or in code generation. The main parser use of the name is
for ES2015 Function.name handling, and this patch also cleans up handling there
by adding a new IsAnonymousFunctionDefinition() method to Expression (the name
comes from the spec).

Also removed unused ParserTraits::DefaultConstructor method.

BUG=v8:3699
LOG=n

Review URL: https://codereview.chromium.org/1647213002

Cr-Commit-Position: refs/heads/master@{#33643}