[analyzer] do not crash with assertion on processing locations of bodyfarmed functions

This addresses an issue introduced in r183451: since
`removePiecesWithInvalidLocations` is called *after* `adjustCallLocations`,
it is not necessary, and in fact harmful, to have this assertion in
adjustCallLocations.

Addresses rdar://36170689

Differential Revision: https://reviews.llvm.org/D41680

llvm-svn: 321682