DEPR/CLN: remove SparseTimeSeries class (follow-up GH15098)

[jorisvandenbossche]

#15098 removed the TimeSeries alias, but we also deprecated SparseTimeSeries (#10890), so this makes the removal complete.

[codecov-io]

Codecov Report

Merging #15567 into master will decrease coverage by -0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #15567      +/-   ##
==========================================
- Coverage   91.07%   91.03%   -0.04%     
==========================================
  Files         136      137       +1     
  Lines       49167    49303     +136     
==========================================
+ Hits        44777    44884     +107     
- Misses       4390     4419      +29

Impacted Files	Coverage Δ
pandas/compat/pickle_compat.py	68.29% <ø> (ø)	✅
pandas/sparse/series.py	95.13% <ø> (-0.06%)	❌
pandas/sparse/api.py	100% <100%> (ø)	✅
pandas/io/gbq.py	25% <0%> (-58.34%)	❌
pandas/util/testing.py	81.11% <0%> (-0.96%)	❌
pandas/tools/merge.py	91.78% <0%> (-0.35%)	❌
pandas/core/frame.py	97.83% <0%> (-0.1%)	❌
pandas/core/generic.py	96.25% <0%> (-0.07%)	❌
pandas/formats/format.py	95.34% <0%> (-0.07%)	❌
pandas/io/json/init.py	100% <0%> (ø)	✅
... and 4 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7ae4fd1...daa7c32. Read the comment docs.

[jreback]

lgtm