* Remove duplicated sha1 implementation (Fixes#6568)
The Hash library had its own copy of a loop-unrolled sha1 implementation
adding a large code footprint for no good reason, as there are several
sha1 implementations already in tree (one in NONOS-SDK as well as one
in bearssl). Switching to the bearssl one is straightforward and removes
about 3kb of code size overhead.
Also cleanup some obvious inefficiencies (copy by value, string
summing, no reservation causing repeated reallocations) in the
implementation.
* Remove overload variants for sha1(...) that accept nonconst data
The data is always remaining unmodified, so non-const overloads
are confusing and redundant. Also optimize the hexify variant
a bit more.
