x86: Remove duplicate TSC DEADLINE MSR definitions

There are two definitions for the TSC deadline MSR in msr-index.h,
one with an underscore and one without.  Axe one of them and move
all the references over to the other one.

 [ bp: Fixup the MSR define in handle_fastpath_set_msr_irqoff() too. ]

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200305174706.0D6B8EE4@viggo.jf.intel.com