Remove redundant instructions from tlb.S

The "_MTC0 v0, COP_0_TLB_HI" is actually incorrect because v0 has not been
initialized at that point. It worked correctly because we subsequently
did the right thing and initialized TLB_HI correctly.

The "li v0, MIPS_KSEG0_START" is redundant because we do exactly the same
thing 2 instructions down.

Approved by: imp (mentor)