[mips] Do not pass redundant IsN64 flag to MCELFObjectTargetWriter. NFC

Now we pass the 'Is64_' flag to the MCELFObjectTargetWriter ctor iif
when we make deal with N64 ABI. So it is redundant to pass additional
'IsN64' flag.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313878 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed