Remove default batch formatter

[FantasticFiasco]

Remove DefaultBatchFormatter in favour of promoting ArrayBatchFormatter to default batch formatter.

Fixes #178

[codecov]

Codecov Report

Merging #235 (fa2c48e) into master (833fca5) will increase coverage by 0.34%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #235      +/-   ##
==========================================
+ Coverage   92.64%   92.98%   +0.34%     
==========================================
  Files          29       28       -1     
  Lines         897      884      -13     
==========================================
- Hits          831      822       -9     
+ Misses         66       62       -4     

Impacted Files	Coverage Δ
...og.Sinks.Http/LoggerSinkConfigurationExtensions.cs	100.00% <100.00%> (ø)
....Http/Sinks/Http/Private/Durable/HttpLogShipper.cs	86.45% <0.00%> (+4.16%)	⬆️

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