Live photo download no longer removes what was at its destination

The image and video are renamed into place, and the rename already
replaces the image's name, so the removal and the test that planted a
ZIP there are gone, along with the comments describing it.

Adds a test for a live photo the content cache recorded with no video,
because it opened before knowing the file is a live photo while no JSON
file named its image and video: original() fetches both again and writes
the JSON file. The comment on that check now names this case.

Model: opus-5-5

test/download/download.test.ts

@@ -1883,15 +1883,6 @@ describe("downloadFile live photos", () => {
         expect(readdirSync(t.dir).sort()).toEqual(["f.JPG", "f.bin"]);
     });
 
-    it("replaces what was at the destination", async () => {
-        const t = setup(livePhotoZip(), livePhoto);
-        writeFileSync(t.outPath, livePhotoZip());
-
-        await t.run();
-
-        expect(readdirSync(t.dir).sort()).toEqual(["f.heic", "f.mov"]);
-    });
-
     it("renames the image and then the video into place, each from its own temp file", async () => {
         const t = setup(livePhotoZip(), livePhoto);