compress/flate: remove var newH

compress/flate: remove var newH

After CL 404696 hewH is no longer used outide the loop and val can be
used inside the loop instead. This leads to another slight improvement
in some benchmarks (only non-zero results reported):

name                             old time/op    new time/op     delta
Decode/Digits/Huffman/1e4-4         125µs ±40%       96µs ± 7%  -22.72%  (p=0.000 n=10+10)
Decode/Digits/Huffman/1e5-4        1.02ms ± 4%     0.97ms ± 3%   -4.29%  (p=0.000 n=10+10)
Decode/Digits/Huffman/1e6-4        10.5ms ± 3%     10.1ms ± 2%   -3.34%  (p=0.000 n=10+9)
Decode/Digits/Speed/1e4-4           130µs ± 5%      119µs ± 3%   -8.33%  (p=0.000 n=10+10)
Decode/Digits/Speed/1e5-4          1.32ms ± 3%     1.26ms ± 4%   -4.14%  (p=0.001 n=10+10)
Decode/Digits/Speed/1e6-4          13.4ms ± 3%     12.8ms ± 3%   -4.64%  (p=0.000 n=10+10)
Decode/Digits/Default/1e4-4         142µs ±19%      124µs ± 3%  -12.75%  (p=0.000 n=10+9)
Decode/Digits/Default/1e5-4        1.33ms ± 4%     1.27ms ± 2%   -4.45%  (p=0.000 n=10+10)
Decode/Digits/Compression/1e4-4     132µs ± 4%      126µs ± 3%   -4.59%  (p=0.000 n=10+10)
Decode/Digits/Compression/1e5-4    1.31ms ± 4%     1.28ms ± 3%   -2.12%  (p=0.015 n=10+10)
Decode/Digits/Compression/1e6-4    13.2ms ± 3%     12.8ms ± 4%   -3.36%  (p=0.000 n=10+10)
Decode/Newton/Huffman/1e4-4         138µs ± 5%      128µs ± 3%   -7.55%  (p=0.000 n=10+9)
Decode/Newton/Huffman/1e5-4        1.25ms ± 1%     1.23ms ± 3%   -2.21%  (p=0.027 n=8+10)
Decode/Newton/Huffman/1e6-4        13.0ms ± 5%     12.2ms ± 5%   -6.54%  (p=0.000 n=10+10)
Decode/Newton/Speed/1e4-4           128µs ± 3%      118µs ± 4%   -7.34%  (p=0.000 n=9+10)
Decode/Newton/Speed/1e5-4          1.06ms ± 3%     1.02ms ± 3%   -3.58%  (p=0.001 n=9+10)
Decode/Newton/Speed/1e6-4          10.4ms ± 4%     10.1ms ± 3%   -3.15%  (p=0.003 n=10+10)
Decode/Newton/Compression/1e4-4     105µs ± 2%      108µs ± 5%   +2.82%  (p=0.043 n=9+10)
Encode/Digits/Speed/1e5-4          1.65ms ± 2%     1.70ms ± 4%   +2.77%  (p=0.003 n=8+10)
Encode/Newton/Default/1e6-4        58.0ms ± 2%     57.0ms ± 1%   -1.59%  (p=0.001 n=9+9)

name                             old speed      new speed       delta
Decode/Digits/Huffman/1e4-4      82.2MB/s ±30%  103.9MB/s ± 8%  +26.38%  (p=0.000 n=10+10)
Decode/Digits/Huffman/1e5-4      98.5MB/s ± 4%  102.9MB/s ± 3%   +4.46%  (p=0.000 n=10+10)
Decode/Digits/Huffman/1e6-4      95.6MB/s ± 3%   98.9MB/s ± 2%   +3.44%  (p=0.000 n=10+9)
Decode/Digits/Speed/1e4-4        76.9MB/s ± 5%   83.8MB/s ± 3%   +9.06%  (p=0.000 n=10+10)
Decode/Digits/Speed/1e5-4        75.8MB/s ± 3%   79.1MB/s ± 4%   +4.34%  (p=0.001 n=10+10)
Decode/Digits/Speed/1e6-4        74.4MB/s ± 3%   78.0MB/s ± 3%   +4.86%  (p=0.000 n=10+10)
Decode/Digits/Default/1e4-4      70.7MB/s ±17%   80.6MB/s ± 2%  +13.93%  (p=0.000 n=10+9)
Decode/Digits/Default/1e5-4      75.4MB/s ± 4%   78.9MB/s ± 3%   +4.60%  (p=0.000 n=10+10)
Decode/Digits/Compression/1e4-4  75.8MB/s ± 3%   79.4MB/s ± 3%   +4.79%  (p=0.000 n=10+10)
Decode/Digits/Compression/1e5-4  76.5MB/s ± 4%   78.1MB/s ± 3%   +2.15%  (p=0.015 n=10+10)
Decode/Digits/Compression/1e6-4  75.7MB/s ± 3%   78.3MB/s ± 4%   +3.49%  (p=0.000 n=10+10)
Decode/Newton/Huffman/1e4-4      72.4MB/s ± 5%   78.3MB/s ± 3%   +8.13%  (p=0.000 n=10+9)
Decode/Newton/Huffman/1e5-4      79.8MB/s ± 1%   81.6MB/s ± 3%   +2.29%  (p=0.026 n=8+10)
Decode/Newton/Huffman/1e6-4      76.9MB/s ± 5%   82.2MB/s ± 5%   +6.96%  (p=0.000 n=10+10)
Decode/Newton/Speed/1e4-4        78.4MB/s ± 3%   84.6MB/s ± 4%   +7.92%  (p=0.000 n=9+10)
Decode/Newton/Speed/1e5-4        94.2MB/s ± 3%   97.7MB/s ± 3%   +3.72%  (p=0.001 n=9+10)
Decode/Newton/Speed/1e6-4        96.0MB/s ± 4%   99.1MB/s ± 3%   +3.24%  (p=0.003 n=10+10)
Decode/Newton/Compression/1e4-4  95.2MB/s ± 2%   92.6MB/s ± 5%   -2.67%  (p=0.043 n=9+10)
Encode/Digits/Speed/1e5-4        60.6MB/s ± 2%   59.0MB/s ± 4%   -2.66%  (p=0.002 n=8+10)
Encode/Newton/Default/1e6-4      17.3MB/s ± 2%   17.5MB/s ± 1%   +1.60%  (p=0.001 n=9+9)

Change-Id: I833b008fe5b67cd17ffdfbec22a3e4b10fcddece
Reviewed-on: https://go-review.googlesource.com/c/go/+/406754
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>