Remove unused JSNAMESPACE_SUPPORT from event-dispatch

[rahatarmanahmed]

This was an old feature that let you add jsnamespace="ns to an element to implicitly add the ns. namespace to all unnamespaced JSAction handlers on or under that element. This required an expensive DOM walk to find the jsnamespace, and almost all JSAction users turned this feature off. The last usage in google 3was removed, so we can delete this now.

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[rahatarmanahmed]

Realized I need to delete references to the flag first even if its unused!

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