Do not return a bool value from error().

error returned true if there was an error. This allows us to replace
the code like this

  if (EC) {
    error(EC, "something failed");
    return;
  }

with

  if (error(EC, "something failed"))
    return;

I thought that that was a good idea, but it turned out that we only
have two places to use this pattern. So this patch removes that feature.

llvm-svn: 263362