Remove unnecessary exports

[thornbill]

These exports really didn't improve the developer experience like I hoped... it just made things confusing to have the same models exported via different paths.

[codecov-commenter]

Codecov Report

Merging #148 (046af32) into master (9a94f5e) will decrease coverage by 16.19%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master     #148       +/-   ##
===========================================
- Coverage   99.76%   83.56%   -16.20%     
===========================================
  Files          17       17               
  Lines         428      426        -2     
  Branches       44       44               
===========================================
- Hits          427      356       -71     
- Misses          1       70       +69     

Impacted Files	Coverage Δ
src/models/api/index.ts	0.00% <ø> (-100.00%)	⬇️
src/models/index.ts	100.00% <ø> (ø)
src/models/api/item-sort-by.ts	0.00% <0.00%> (-100.00%)	⬇️
src/models/api/base-item-kind.ts	0.00% <0.00%> (-100.00%)	⬇️

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