removed is_activated as it's unused

[Wikunia]

I was mainly confused why I have is_activated and is_deactivated inside #213 and saw that is_activated isn't used anymore.
This PR removes all is_activated as it was only set but never used somewhere.

[codecov]

Codecov Report

Merging #284 (cec5c62) into master (72f4c36) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #284      +/-   ##
==========================================
- Coverage   97.62%   97.61%   -0.01%     
==========================================
  Files          52       52              
  Lines        4328     4326       -2     
==========================================
- Hits         4225     4223       -2     
  Misses        103      103              

Impacted Files	Coverage Δ
src/constraints.jl	100.00% <ø> (ø)
src/type_inits.jl	96.29% <ø> (ø)
src/types.jl	99.00% <ø> (ø)
src/util.jl	98.44% <ø> (-0.02%)	⬇️

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