Patch to remove libsvn_ra_neon

We've had the "should we remove neon?" discussion before, and the
consensus has felt to resolve in the affirmative. Now is the time for
action.

I've got a 586 kb patch which removes libsvn_ra_neon from trunk. It
doesn't not remove the --http-library runtime option or config file
code, but does remove the various build stuff which supports building
neon. I obviously haven't tested this on all platforms, and I
wouldn't be surprised if it causes some short-term breakage. My plan
is to commit this patch Real Soon Now, pending any very vocal
objections from folks on this list.

-Hyrum

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