The gold plugin doesn't need disassemblers.

Back in r128440 tools/LTO started exporting the disassembler interface. It
was never clear why, but whatever the reason I am pretty sure it doesn't hold
for tools/gold.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211325 91177308-0d34-0410-b5e6-96231b3b80d8