[pm] remove deprecated mOldCodePaths in PackageSetting

This is not used anywhere (presumably it was used at one point to
preserve the old paths during DONT_KILL installs, but unclear).

If needed, oldPackage.getPath() returns the replaced package's path, so
we can just use that.

BUG: 291212866
Test: n/a

Change-Id: I7aa7cc970835fb8bd92ace189841728b455689ee