The TSS no longer needs to be unbusied before loading the task register,
since the set_tss_desc macros set the system gate type to Available IA-32 TSS.
This obscure, uncommented legacy code can now be removed for better
readability and saves 20 bytes of code space. 

Here is a breakdown of __set_tss_desc + load_TR before and after.  The
doublefault TSS GDT setup has similar savings.

- Zachary Amsden (zach@vmware.com)

before:
c01d4535:       ba 80 20 1b c0          mov    $0xc01b2080,%edx
c01d453a:       b8 00 d8 1c c0          mov    $0xc01cd800,%eax
c01d453f:       66 c7 42 00 eb 00       movw   $0xeb,0x0(%edx)
c01d4545:       66 89 42 02             mov    %ax,0x2(%edx)
c01d4549:       c1 c8 10                ror    $0x10,%eax
c01d454c:       88 42 04                mov    %al,0x4(%edx)
c01d454f:       c6 42 05 89             movb   $0x89,0x5(%edx)
                                                  ^^ non-busy
c01d4553:       c6 42 06 00             movb   $0x0,0x6(%edx)
c01d4557:       88 62 07                mov    %ah,0x7(%edx)
c01d455a:       c1 c8 10                ror    $0x10,%eax
c01d455d:       81 25 84 20 1b c0 ff    andl   $0xfffffdff,0xc01b2084
c01d4564:       fd ff ff
c01d4567:       b8 80 00 00 00          mov    $0x80,%eax
c01d456c:       0f 00 d8                ltr    %ax

now:
c01d4535:       ba 80 20 1b c0          mov    $0xc01b2080,%edx
c01d453a:       b8 00 d8 1c c0          mov    $0xc01cd800,%eax
c01d453f:       66 c7 42 00 eb 00       movw   $0xeb,0x0(%edx)
c01d4545:       66 89 42 02             mov    %ax,0x2(%edx)
c01d4549:       c1 c8 10                ror    $0x10,%eax
c01d454c:       88 42 04                mov    %al,0x4(%edx)
c01d454f:       c6 42 05 89             movb   $0x89,0x5(%edx)
c01d4553:       c6 42 06 00             movb   $0x0,0x6(%edx)
c01d4557:       88 62 07                mov    %ah,0x7(%edx)
c01d455a:       c1 c8 10                ror    $0x10,%eax
c01d455d:       b8 80 00 00 00          mov    $0x80,%eax
c01d4562:       0f 00 d8                ltr    %ax