Prune unused local variable.
<rdar://problem/15191078>

Fixed Module::ResolveSymbolContextForAddress() to be able to also look in the SymbolVendor's SymbolFile's ObjectFile for a more meaningful symbol when a symbol lookup finds a synthetic symbol from the main object file. This will help lookups on MacOSX as the main executable might be stripped, but the dSYM file always has a full symbol table.