[Refactoring] Make finish() of CodeGeneratorJS.pm empty

[Refactoring] Make finish() of CodeGeneratorJS.pm empty
https://bugs.webkit.org/show_bug.cgi?id=76846

Reviewed by Adam Barth.

This is one of steps to stop rebuilding .h/.cpp files generated
by unchanged IDLs (bug 76836).

As a refactoring, we are planning to remove finish() from all
CodeGenerators. In this bug, we make finish() of CodeGeneratorJS.pm
empty.

No new tests. No change in behavior.

* bindings/scripts/CodeGeneratorJS.pm:
(finish): Made it empty. We will remove finish() after
making finish() of all CodeGenerators empty.
(GenerateInterface): Modified to call WriteData().
(WriteData): Simple code refactoring.
Removed if(defined $IMPL).
Removed if(defined $HEADER).
Removed if(defined $DEPS).
$IMPL -> IMPL.
$HEADER -> HEADER.
$DEPS -> DEPS.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@105683 268f45cc-cd09-0410-ab3c-d52691b4dbfc