keyutils-raw: remove usage of libkeyutils

[mathstuf]

Fixes: #24

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Cc: @josephlr @dlrobertson

[codecov]

Codecov Report

Merging #43 into master will decrease coverage by 1.60%.
The diff coverage is 63.04%.

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
- Coverage   88.21%   86.60%   -1.61%     
==========================================
  Files          33       34       +1     
  Lines        2002     2105     +103     
==========================================
+ Hits         1766     1823      +57     
- Misses        236      282      +46     

Impacted Files	Coverage Δ
keyutils-raw/src/types.rs	0.00% <ø> (ø)
src/api.rs	67.37% <58.49%> (-4.62%)	⬇️
keyutils-raw/src/functions.rs	66.93% <66.93%> (ø)

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