[Binding] remove unused #if in idl

This patch remove #if ENABLED(NOTIFICATIONS)...
in ENABLED(NOTIFICATIONS) || ENABLED(LEGACY_NOTIFICATIONS) block.

This change is OK because there is no situation
where !ENABLE(NOTIFICATIONS) and ENABLE(LEGACY_NOTIFICATIONS)
currently and in the future.
(LEGACY_NOTIFICATIONS is going to be removed)

Therefore ENABLE(NOTIFICATIONS) is always true
if ENABLE(NOTIFICATIONS) || ENABLE(LEGACY_NOTIFICATIONS),


Context of this CL: The objective of this CL is to remove this #if. We are 
currently working on replacing all #if macros in IDL files with [Conditional] 
and thus getting rid of preprocessors from the IDL compiler. Since we don't yet 
have a mechanism to support [Conditional] for constructors, we want to remove 
this #if in this CL. 

Generated code is exactly same as before.

R=haraken@chromium.org 
BUG=239771
TEST=No tests. Refactoring.

Review URL: https://chromiumcodereview.appspot.com/17488002

git-svn-id: svn://svn.chromium.org/blink/trunk@152937 bbb929c8-8fbe-4397-9dbb-9b2b20218538