The WeakMap shim should use the built-in version if available.
The WeakMap shim should use the built-in version if available.

Firefox and IE11 have built-in support, so we can skip all this workaround junk.  Also comment out some parts of the shim that we don't actually need (NodeJS & global versions, and a createStorage helper function).

wallw-bits/cesium,likangning93/cesium,jasonbeverage/cesium,kaktus40/cesium,oterral/cesium,CesiumGS/cesium,jasonbeverage/cesium,omh1280/cesium,geoscan/cesium,oterral/cesium,aelatgt/cesium,kaktus40/cesium,likangning93/cesium,omh1280/cesium,likangning93/cesium,AnalyticalGraphicsInc/cesium,aelatgt/cesium,YonatanKra/cesium,oterral/cesium,jason-crow/cesium,ggetz/cesium,AnimatedRNG/cesium,YonatanKra/cesium,NaderCHASER/cesium,CesiumGS/cesium,jason-crow/cesium,kiselev-dv/cesium,likangning93/cesium,esraerik/cesium,emackey/cesium,esraerik/cesium,denverpierce/cesium,AnimatedRNG/cesium,progsung/cesium,NaderCHASER/cesium,NaderCHASER/cesium,josh-bernstein/cesium,jason-crow/cesium,omh1280/cesium,emackey/cesium,wallw-bits/cesium,YonatanKra/cesium,soceur/cesium,soceur/cesium,aelatgt/cesium,AnimatedRNG/cesium,AnalyticalGraphicsInc/cesium,ggetz/cesium,hodbauer/cesium,soceur/cesium,jason-crow/cesium,aelatgt/cesium,progsung/cesium,denverpierce/cesium,denverpierce/cesium,esraerik/cesium,kiselev-dv/cesium,geoscan/cesium,CesiumGS/cesium,esraerik/cesium,denverpierce/cesium,emackey/cesium,YonatanKra/cesium,likangning93/cesium,kiselev-dv/cesium,wallw-bits/cesium,josh-bernstein/cesium,omh1280/cesium,CesiumGS/cesium,kiselev-dv/cesium,AnimatedRNG/cesium,ggetz/cesium,CesiumGS/cesium,hodbauer/cesium,hodbauer/cesium,ggetz/cesium,wallw-bits/cesium,emackey/cesium