simplify encodeURI using HttpUtility

[jhgbrt]

This simplifies the encodeURI function, using HttpUtility instead of Uri. Tests pass. I suspect this also to be more performant (although I didn't test this specifically).

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[jhgbrt]

I signed it

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[jhgbrt]

kthxbye

[jhgbrt]

I have signed the CLA, but googlebot insists I have not...

[NeilFraser]

For the record, "jhgbrt" is logged as having signed the CLA. I'm satisfied that the legalities are taken care of, regardless of what our (slightly inflexible and possibly drunk) googlebot thinks.