Enable hardware CRC32 under Valgrind

Copy of https://bugs.mysql.com/bug.php?id=94121:

[29 Jan 15:54] Laurynas Biveinis
Description:
Under Valgrind, hardware CRC32 checksums are disabled because:

static bool ut_crc32_check_cpu() {
...
/* Valgrind does not understand the CRC32 instructions:

vex amd64->IR: unhandled instruction bytes: 0xF2 0x48 0xF 0x38 0xF0 0xA
valgrind: Unrecognised instruction at address 0xad3db5.
...

This comes right from original implementation in 2011. But Valgrind 3.6.1, released also in 2011, added support for the instruction. Eight years later, it should be safe to remove, might save a cycle or two, also the patch only deletes code, which is always good. Quick test with new Valgrind shows that it works.

How to repeat:
See above

Suggested fix:
Remove #ifdef UNIV_DEBUG_VALGRIND from ut_crc32_check_cpu