091d614aad bitcoin: Remove "std" feature from examples (Tobin C. Harding)
Pull request description:
The "rand-std" feature enables "std" but we use it in examples still. FTR I added this a while ago thinking the explicitness was clearer but in hindsight I think that was wrong and that it makes usage of our features _less_ clear.
No logic changes.
(Pulled out of #2756.)
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storopoli:
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apoelstra:
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Tree-SHA512: d72eec37e3a434a1f850cb4257529fc18540cb5075bc7d3bd494cba59b08404c6c86223361a3c3a3de8d50a1168b656ff1123d28f7d2dcdf05c404caff716b1a