Revert "libstore: use makeTempSiblingPath in replaceValidPath"

Revert submission 3850

Reason for revert: caused multiple regressions noticed in https://git.lix.systems/lix-project/lix/issues/975 and https://git.lix.systems/lix-project/lix/issues/966 (suspected).

Root cause analysis has not been done yet and this breaks Lix on Darwin on HEAD.

Reverted changes: /q/submissionid:3850

Change-Id: I23f659664bcb1f38ea8cd053279d3275f33e001c

lix/libstore/build/derivation-goal.cc

@@ -762,7 +762,7 @@ void replaceValidPath(const Path & storePath, const Path & tmpPath)
     Path oldPath;
     if (pathExists(storePath)) {
         do {
-            oldPath = makeTempSiblingPath(storePath);
+            oldPath = makeTempPath(storePath, ".old");
             // store paths are often directories so we can't just unlink() it
             // let's make sure the path doesn't exist before we try to use it
         } while (pathExists(oldPath));