[WebAssembly] Inline translateVA as it's trivial.

The problem I want to address now is that chunks have too many data
members for "offsets", and their origins are not well defined.
For example, InputSegment has OutputSegmentOffset, but it's base class
also has OutputOffset. That's very confusing.

Differential Revision: https://reviews.llvm.org/D43726

llvm-svn: 326291