Remove sk_memcpy32
It's only implemented on x86, where the exisiting benchmark says memcpy() is
faster for all cases:
Timer overhead: 24ns
curr/maxrss loops min median mean max stddev samples config bench
10/10 MB 1 35.9µs 36.2µs 36.2µs 36.6µs 1% ▁▂▄▅▅▃█▄▄▅ nonrendering sk_memcpy32_100000
10/10 MB 13 2.27µs 2.28µs 2.28µs 2.29µs 0% █▄▃▅▃▁▃▅▁▄ nonrendering sk_memcpy32_10000
11/11 MB 677 91.6ns 95.9ns 94.5ns 99.4ns 3% ▅▅▅▅▅█▁▁▁▁ nonrendering sk_memcpy32_1000
11/11 MB 1171 20ns 20.9ns 21.3ns 23.4ns 6% ▁▁▇▃▃▃█▇▃▃ nonrendering sk_memcpy32_100
11/11 MB 1952 14ns 14ns 14.3ns 15.2ns 3% ▁▁██▁▁▁▁▁▁ nonrendering sk_memcpy32_10
11/11 MB 5 33.6µs 33.7µs 34.1µs 35.2µs 2% ▆▇█▁▁▁▁▁▁▁ nonrendering memcpy32_memcpy_100000
11/11 MB 18 2.12µs 2.22µs 2.24µs 2.39µs 5% ▂█▄▇█▄▇▁▁▁ nonrendering memcpy32_memcpy_10000
11/11 MB 1112 87.3ns 87.3ns 89.1ns 93.7ns 3% ▄██▄▁▁▁▁▁▁ nonrendering memcpy32_memcpy_1000
11/11 MB 2124 12.8ns 13.3ns 13.5ns 14.8ns 6% ▁▁▁█▃▃█▇▃▃ nonrendering memcpy32_memcpy_100
11/11 MB 3077 9ns 9.41ns 9.52ns 10.2ns 4% ▃█▁█▃▃▃▃▃▃ nonrendering memcpy32_memcpy_10
(Why? One fewer thing to port to SkOpts.)
BUG=skia:4117
Review URL: https://codereview.chromium.org/
1256763003