Delete 108 lines of ASM from vmx_enter_guest() that predated lots

Delete 108 lines of ASM from vmx_enter_guest() that predated lots
of later enhancements, removing the save/restore of flags, selectors,
and MSRs: flags are caller-saved and don't need restoring while
selectors and MSRs are auto-restored.  The FSBASE, GSBASE, and
KERNELGSBASE MSRs just need the correct values set with vmwrite()
in the "on new CPU?" block of vcpu_run_vmx().

Also, only rdmsr(MSR_MISC_ENABLE) once in vcpu_reset_regs_vmx(),
give symbolic names to the exit-load MSR slots, eliminate
VMX_NUM_MSR_STORE, and #if 0 the vc_vmx_msr_entry_load_{va,pa} code
and definitions as unused.

ok dv@