compress/flate: remove compressor.hash field
compress/flate: remove compressor.hash field

After CL 20929, the only remaining uses of d.hash are immediately
after it is set.

Benchmarks where benchstat reports a non-zero delta:

name                              old time/op    new time/op    delta
Decode/Newton/Huffman/1e5-12         982µs ± 6%     922µs ± 4%  -6.12%  (p=0.000 n=10+10)
Decode/Newton/Huffman/1e6-12        8.14ms ± 2%    7.71ms ± 2%  -5.19%  (p=0.000 n=10+10)
Encode/Digits/Huffman/1e5-12         241µs ± 0%     239µs ± 0%  -0.62%  (p=0.000 n=9+10)
Encode/Digits/Speed/1e4-12           113µs ± 0%     114µs ± 0%  +1.21%  (p=0.000 n=9+8)
Encode/Digits/Speed/1e5-12          1.04ms ± 0%    1.05ms ± 0%  +0.22%  (p=0.027 n=9+8)
Encode/Digits/Speed/1e6-12          10.3ms ± 0%    10.3ms ± 0%  +0.16%  (p=0.036 n=9+8)
Encode/Digits/Default/1e4-12         193µs ± 0%     195µs ± 1%  +0.77%  (p=0.010 n=8+8)
Encode/Digits/Default/1e5-12        2.92ms ± 1%    2.93ms ± 0%  +0.54%  (p=0.002 n=8+8)
Encode/Digits/Compression/1e4-12     193µs ± 0%     194µs ± 0%  +0.67%  (p=0.000 n=8+8)
Encode/Digits/Compression/1e5-12    2.92ms ± 0%    2.93ms ± 0%  +0.53%  (p=0.002 n=8+8)
Encode/Digits/Compression/1e6-12    31.0ms ± 1%    31.2ms ± 0%  +0.80%  (p=0.000 n=10+9)
Encode/Newton/Huffman/1e4-12        34.8µs ± 1%    34.3µs ± 0%  -1.31%  (p=0.000 n=9+10)
Encode/Newton/Huffman/1e5-12         294µs ± 0%     291µs ± 0%  -1.09%  (p=0.000 n=8+9)
Encode/Newton/Huffman/1e6-12        2.91ms ± 0%    2.89ms ± 0%  -0.89%  (p=0.000 n=8+9)
Encode/Newton/Speed/1e5-12           838µs ± 0%     836µs ± 0%  -0.18%  (p=0.015 n=8+8)
Encode/Newton/Speed/1e6-12          8.35ms ± 0%    8.28ms ± 1%  -0.89%  (p=0.000 n=8+10)
Encode/Newton/Default/1e5-12        3.55ms ± 0%    3.54ms ± 0%  -0.23%  (p=0.027 n=8+9)
Encode/Newton/Default/1e6-12        37.4ms ± 0%    37.3ms ± 0%  -0.18%  (p=0.001 n=9+8)
Encode/Newton/Compression/1e6-12    53.3ms ± 0%    53.1ms ± 0%  -0.25%  (p=0.010 n=10+9)

name                              old speed      new speed      delta
Decode/Newton/Huffman/1e5-12       102MB/s ± 6%   109MB/s ± 4%  +6.48%  (p=0.000 n=10+10)
Decode/Newton/Huffman/1e6-12       123MB/s ± 2%   130MB/s ± 2%  +5.49%  (p=0.000 n=10+10)
Encode/Digits/Huffman/1e5-12       416MB/s ± 0%   418MB/s ± 0%  +0.62%  (p=0.000 n=9+10)
Encode/Digits/Speed/1e4-12        88.9MB/s ± 0%  87.8MB/s ± 0%  -1.19%  (p=0.000 n=9+8)
Encode/Digits/Speed/1e5-12        95.7MB/s ± 0%  95.5MB/s ± 0%  -0.22%  (p=0.025 n=9+8)
Encode/Digits/Speed/1e6-12        97.5MB/s ± 0%  97.3MB/s ± 0%  -0.16%  (p=0.026 n=9+8)
Encode/Digits/Default/1e4-12      51.7MB/s ± 0%  51.3MB/s ± 1%  -0.76%  (p=0.007 n=8+8)
Encode/Digits/Default/1e5-12      34.3MB/s ± 1%  34.1MB/s ± 0%  -0.54%  (p=0.001 n=8+8)
Encode/Digits/Compression/1e4-12  51.8MB/s ± 0%  51.5MB/s ± 0%  -0.66%  (p=0.000 n=8+8)
Encode/Digits/Compression/1e5-12  34.3MB/s ± 0%  34.1MB/s ± 0%  -0.53%  (p=0.002 n=8+8)
Encode/Digits/Compression/1e6-12  32.3MB/s ± 1%  32.0MB/s ± 0%  -0.79%  (p=0.000 n=10+9)
Encode/Newton/Huffman/1e4-12       288MB/s ± 1%   291MB/s ± 0%  +1.33%  (p=0.000 n=9+10)
Encode/Newton/Huffman/1e5-12       340MB/s ± 0%   344MB/s ± 0%  +1.10%  (p=0.000 n=8+9)
Encode/Newton/Huffman/1e6-12       343MB/s ± 0%   346MB/s ± 0%  +0.90%  (p=0.000 n=8+9)
Encode/Newton/Speed/1e5-12         119MB/s ± 0%   120MB/s ± 0%  +0.18%  (p=0.014 n=8+8)
Encode/Newton/Speed/1e6-12         120MB/s ± 0%   121MB/s ± 1%  +0.90%  (p=0.000 n=8+10)
Encode/Newton/Default/1e5-12      28.2MB/s ± 0%  28.3MB/s ± 0%  +0.23%  (p=0.029 n=8+9)
Encode/Newton/Default/1e6-12      26.7MB/s ± 0%  26.8MB/s ± 0%  +0.20%  (p=0.000 n=9+7)
Encode/Newton/Compression/1e6-12  18.8MB/s ± 0%  18.8MB/s ± 0%  +0.25%  (p=0.012 n=10+9)

Change-Id: I8ba0efcf5d42595d856082656b45f87bb3d7be0f
Reviewed-on: https://go-review.googlesource.com/c/go/+/404696
Auto-Submit: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>
Reviewed-by: Joseph Tsai <ad9e03fbec35106ba742f446a098eef3d5e31d20@digital-static.net>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>

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