remove lazy-pos forceValue

almost all uses of this are interactive, except for deepSeq. deepSeq is
going to be expensive and rare enough to not care much about, and
Value::determinePos should usually be cheap enough to not be too much of
a burden in any case.

src/nix-build/nix-build.cc

@@ -350,7 +350,7 @@ static void main_nix_build(int argc, char * * argv)
                 takesNixShellAttr(vRoot) ? *autoArgsWithInNixShell : *autoArgs,
                 vRoot
             ).first);
-            state->forceValue(v, [&]() { return v.determinePos(noPos); });
+            state->forceValue(v, v.determinePos(noPos));
             getDerivations(
                 *state,
                 v,