Fix -Wdocumentation warning (@returns used in void function). NFCI.

/// Removes all the Defined Functions (as well as their calls)

/// that aren't inside any of the desired Chunks.

/// @returns the Module stripped of out-of-chunk functions

static void extractFunctionsFromModule(const std::vector<Chunk> &ChunksToKeep,

                                       Module *Program) {

  // Get functions inside desired chunks