[ELF] - Eliminate dead "if". NFC.

We call switchTo() from assignAddresses() for switching to Aether,
and from assignOffsets().

First calls assignOffsets() one by one for each output section.
(https://github.com/llvm-mirror/lld/blob/master/ELF/LinkerScript.cpp#L1045)

That I believe means the condition removed in this patch is dead.

llvm-svn: 336356