Remove deprecated interfaces

[JensAyton]

This has been deprecated for over two years.

If we merge this it’s a semver MAJOR change, so I guess the question is if we want anything else in a 2.0.0 release.

@rastersize @8W9aG @dflems

[codecov-io]

Codecov Report

Merging #103 into master will decrease coverage by 0.32%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #103      +/-   ##
==========================================
- Coverage   99.27%   98.94%   -0.33%     
==========================================
  Files          14       14              
  Lines         964      952      -12     
==========================================
- Hits          957      942      -15     
- Misses          7       10       +3

Impacted Files	Coverage Δ
Sources/SPTPersistentCacheOptions.m	100% <ø> (ø)	⬆️
Sources/SPTPersistentCache.m	99.05% <0%> (-0.48%)	⬇️

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[8W9aG]

I think we can bump the semver here, nothing else I would like to add in

[dflems]

Looking through the internal bug tracker, we don't seem to have any open tickets. Maybe we could do some of the smaller feature requests.

[dflems]

@JensAyton: I just got this project happy with Xcode 10 if you care to revive this.