Use libsecp256k1 instead of OpenSSL for key derivation:

While most of the code associated with secp256k1 operations had
been migrated to libsecp256k1, the deterministic key derivation
code was still using calls to OpenSSL.

If merged, this commit replaces the OpenSSL-based routines with
new libsecp256k1-based implementations. No functional change is
expected and the change should be transparent.

This commit also removes several support classes and utility
functions that wrapped or adapted various OpenSSL types that
are no longer needed.

A tip of the hat to the original author of this truly superb
library, Dr. Pieter Wuille, and to all other contributors.

Builds/levelization/results/loops.txt

@@ -34,9 +34,6 @@ Loop: ripple.basics ripple.rpc
 Loop: ripple.core ripple.net
   ripple.net > ripple.core
 
-Loop: ripple.crypto ripple.protocol
-  ripple.protocol > ripple.crypto
-
 Loop: ripple.net ripple.rpc
   ripple.rpc > ripple.net
 

Builds/levelization/results/ordering.txt

@@ -48,6 +48,7 @@ ripple.peerfinder > ripple.beast
 ripple.peerfinder > ripple.core
 ripple.peerfinder > ripple.protocol
 ripple.protocol > ripple.beast
+ripple.protocol > ripple.crypto
 ripple.protocol > ripple.json
 ripple.resource > ripple.basics
 ripple.resource > ripple.beast
@@ -117,8 +118,6 @@ test.core > ripple.server
 test.core > test.jtx
 test.core > test.toplevel
 test.core > test.unit_test
-test.crypto > ripple.beast
-test.crypto > ripple.crypto
 test.csf > ripple.basics
 test.csf > ripple.beast
 test.csf > ripple.consensus