* Remove word_swap_longword.
This was the same as `swapx` and not used except in one place which
now uses `swapx` instead.
* Remove assembly versions of swapx, byte_swap_word, word_swap_page.
`swapx` and `byte_swap_word` were defined as:
```
extern inline const unsigned int swapx (unsigned int word)
{
asm("roll $16,%0" : "=g" (word) : "0" (word));
return(word);
}
extern inline const unsigned short byte_swap_word (unsigned short word)
{
asm("rolw $8,%0" : "=r" (word) : "0" (word));
return(word);
}
```
But the generated code from the C version is:
```
(lldb) disassemble -n swapx
ldex`swapx:
ldex[0x10002e0d0] <+0>: pushq %rbp
ldex[0x10002e0d1] <+1>: movq %rsp, %rbp
ldex[0x10002e0d4] <+4>: movl %edi, %eax
ldex[0x10002e0d6] <+6>: roll $0x10, %eax
ldex[0x10002e0d9] <+9>: popq %rbp
ldex[0x10002e0da] <+10>: retq
(lldb) disassemble -n byte_swap_word
ldex`byte_swap_word:
ldex[0x10002e0e0] <+0>: pushq %rbp
ldex[0x10002e0e1] <+1>: movq %rsp, %rbp
ldex[0x10002e0e4] <+4>: rolw $0x8, %di
ldex[0x10002e0e8] <+8>: movzwl %di, %eax
ldex[0x10002e0eb] <+11>: popq %rbp
ldex[0x10002e0ec] <+12>: retq
```
So we don't really stand to gain by re-enabling this old assembler code.
We would gain from switching to C99 or C11 and improving our
inlining.
* Remove 386 asm version of bit_reverse_region.
This is implemented in C and the code isn't actually set up to
allow using the assembler version.
