In \crossref{sproutspendingkeyencoding}, remove the statement that future key representations might use the padding bits of Sprout spending keys.
In \crossref{sproutspendingkeyencoding}, remove the statement that future key representations
might use the padding bits of Sprout spending keys.

Signed-off-by: Daira Hopwood <cd7d43d5556a38ce626d53826fddc46adc597539@jacaranda.org>

zcash/zips,zcash/zips,zcash/zips,zcash/zips