crypto: consistent api across keys

[tac0turtle]

Description

This Pr changes GenPrivKeySecp256k1 to GenPrivKeyFromSecret to be consistent with the other keys. Also the previous name was not descriptive on what it did.

Closes: #XXX

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[codecov]

Codecov Report

Merging #5214 into master will increase coverage by 1.60%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #5214      +/-   ##
==========================================
+ Coverage   60.87%   62.47%   +1.60%     
==========================================
  Files         203      259      +56     
  Lines       20369    27110    +6741     
==========================================
+ Hits        12400    16938    +4538     
- Misses       6905     8700    +1795     
- Partials     1064     1472     +408     

Impacted Files	Coverage Δ
crypto/secp256k1/secp256k1.go	63.63% <100.00%> (ø)
blockchain/v0/reactor.go	65.11% <0.00%> (-4.66%)	⬇️
consensus/reactor.go	75.11% <0.00%> (-0.47%)	⬇️
proxy/multi_app_conn.go	58.02% <0.00%> (ø)
p2p/base_reactor.go	81.81% <0.00%> (ø)
light/rpc/client.go	0.00% <0.00%> (ø)
privval/signer_endpoint.go	81.57% <0.00%> (ø)
mempool/metrics.go	16.66% <0.00%> (ø)
p2p/pex/pex_reactor.go	80.95% <0.00%> (ø)
libs/tempfile/tempfile.go	81.39% <0.00%> (ø)
... and 54 more