[new compiler] Fix memory leaks

[new compiler] Fix memory leaks

In memory pool allocated classes we cannot have members that require a
destructor to run to free memory. Therefore this patch removes the QSets in the
object class used for duplicate property and signal name checking. The checking
is instead done using linear search, which should be fine given that usually
the number declared signals and newly declared properties is low per type.

Change-Id: Id7a7a9bdd9e145975dcee4d5340489615f4f71e3
Reviewed-by: Lars Knoll <lars.knoll@digia.com>