Remove hwrand_initialized.
Summary:
All access to hwrand is now gated by GetRNGState, which initializes the hwrand code.
Partial backport of Core PR14955
https://github.com/bitcoin/bitcoin/pull/14955/commits/4ea8e50837a0932b31a241988fd68d6730a2048a
Depends on D4396
Test Plan:
make check
Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc
Reviewed By: Fabien, O1 Bitcoin ABC, #bitcoin_abc
Differential Revision: https://reviews.bitcoinabc.org/D4397