Delete unnecessary FingerprintUpdatingReader

[djaglowski]

As part of an ongoing effort to simplify the file_input operator, this PR removes a struct called FingerprintUpdatingReader. This struct wrapped a Reader and managed the Reader fingerprint. However, a Reader can manage its own fingerprint just fine.

[codecov]

Codecov Report

Merging #202 (53ea0b8) into main (d485c45) will decrease coverage by 0.0%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main    #202     +/-   ##
=======================================
- Coverage   75.7%   75.6%   -0.1%     
=======================================
  Files         95      95             
  Lines       4406    4399      -7     
=======================================
- Hits        3336    3329      -7     
  Misses       743     743             
  Partials     327     327             

Impacted Files	Coverage Δ
operator/builtin/input/file/reader.go	64.5% <100.0%> (-2.5%)	⬇️

[djaglowski]

Benchmarks on main:

BenchmarkFileInput/Single-8               607011              2037 ns/op             752 B/op         14 allocs/op
BenchmarkFileInput/Glob-8                 111948             10901 ns/op            3019 B/op         58 allocs/op
BenchmarkFileInput/MultiGlob-8            111188             10920 ns/op            3019 B/op         58 allocs/op
BenchmarkFileInput/MaxConcurrent-8         58669             17186 ns/op            3013 B/op         58 allocs/op
BenchmarkFileInput/FngrPrntLarge-8        461990              2227 ns/op             753 B/op         14 allocs/op
BenchmarkFileInput/FngrPrntSmall-8        458853              2229 ns/op             752 B/op         14 allocs/op

Benchmarks on this branch:

BenchmarkFileInput/Single-8               598479              2032 ns/op             752 B/op         14 allocs/op
BenchmarkFileInput/Glob-8                 114415             10666 ns/op            3019 B/op         58 allocs/op
BenchmarkFileInput/MultiGlob-8            113360             10785 ns/op            3019 B/op         58 allocs/op
BenchmarkFileInput/MaxConcurrent-8         58641             17157 ns/op            3013 B/op         58 allocs/op
BenchmarkFileInput/FngrPrntLarge-8        617730              2270 ns/op             753 B/op         14 allocs/op
BenchmarkFileInput/FngrPrntSmall-8        471415              2176 ns/op             752 B/op         14 allocs/op