DEPR: Deprecate SparseList
Title is self-explanatory.  Closes #13784.

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14007?src=pr) is 85.28% (diff: 100%)

> Merging [#14007](https://codecov.io/gh/pydata/pandas/pull/14007?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **<.01%**

``` diff
@@             master     #14007   diff @@
==========================================
  Files           139        139          
  Lines         50229      50231     +2   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          42837      42840     +3   
+ Misses         7392       7391     -1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [8b50d8c...f1ce0e9](https://codecov.io/gh/pydata/pandas/compare/8b50d8c854196e3025c9a881cafeedc5f509aaef...f1ce0e926394eaf5c416de61e9078aaf2f1cd554?src=pr)
 thanks!
