Remvoe all getproperty funcs

[inkydragon]

Close #77

I've checked all SHA2_CTX and SHA3_CTX subtypes usage by using JuliaHub.

Only a few packages use SHA.jl directly.
All packages use only the exported API.
So it seems safe to remove this code.

To be on the safe side, we could run pkg-eval the next time you update the SHA version in julia.

• https://juliahub.com/ui/Search?q=SHA2_256_CTX&type=symbols
• https://juliahub.com/ui/Search?q=SHA2_512_CTX&type=symbols
• https://juliahub.com/ui/Search?q=SHA256_CTX&type=symbols

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (4ab324c) 99.79% compared to head (63817ab) 99.78%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #99      +/-   ##
==========================================
- Coverage   99.79%   99.78%   -0.01%     
==========================================
  Files           9        9              
  Lines         490      468      -22     
==========================================
- Hits          489      467      -22     
  Misses          1        1              

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