Avoid pointless refcounting in array_reduce

[nielsdos]

For this script:

for ($i=0;$i < 100; $i++)
    array_reduce(range(1, 100000), fn ($a,$b)=>$a+$b,1);

On an i7-4790:

Benchmark 1: ./sapi/cli/php reduce_bench.php
  Time (mean ± σ):     272.0 ms ±   3.7 ms    [User: 268.9 ms, System: 2.1 ms]
  Range (min … max):   268.9 ms … 281.3 ms    11 runs

Benchmark 2: ./sapi/cli/php_old reduce_bench.php
  Time (mean ± σ):     288.2 ms ±   3.5 ms    [User: 284.5 ms, System: 2.7 ms]
  Range (min … max):   285.0 ms … 295.9 ms    10 runs

Summary
  ./sapi/cli/php reduce_bench.php  ran
    1.06 ± 0.02 times faster than ./sapi/cli/php_old reduce_bench.php

On an i7-1185G7:

Benchmark 1: ./sapi/cli/php test.php
  Time (mean ± σ):     189.6 ms ± 3.5 ms [User: 178.5 ms, System: 10.7 ms]
  Range (min … max):   187.3 ms … 201.6 ms 15 runs

Benchmark 2: ./sapi/cli/php_old test.php
  Time (mean ± σ):     204.2 ms ± 2.9 ms [User: 190.1 ms, System: 13.6 ms]
  Range (min … max):   200.6 ms … 210.2 ms 14 runs

Summary
  ./sapi/cli/php test.php ran
    1.08 ± 0.02 times faster than ./sapi/cli/php_old test.php

[TimWolla]

At this point it would probably be appropriate to mention this in UPGRADING:

php-src/UPGRADING

Line 410 in 5dd9b0d

14. Performance Improvements

All of the callback-based array functions got performance improvements now, no?

[nielsdos]

All of the callback-based array functions got performance improvements now, no?

Don't know if I missed any important one, but I guess so.