fix(PictureThumbnail): Remove ineffective lazy loading

Setting image.loading = "lazy" after image.src starts the fetch was a
no-op. The loading attribute is consulted before fetch begins, and for
detached Image instances the fetch starts immediately when src is set.
The attribute never actually deferred anything here. Removing it makes
the code honest about what happens and prevents accidental activation
if the order is ever reversed in a context where lazy would be harmful,
such as the crop dialog.

Author: tvdeyen

app/assets/builds/alchemy/alchemy_admin.min.js

@@ -43,7 +43,6 @@ export default class PictureThumbnail extends HTMLElement {
     if (alt) {
       this.image.alt = alt
     }
-    this.image.loading = "lazy"
   }
 
   start(src) {

app/assets/builds/alchemy/alchemy_admin.min.js.map

@@ -152,16 +152,6 @@ describe("alchemy-picture-thumbnail", () => {
       expect(element.image.alt).not.toBe("Test image")
     })
 
-    it("sets loading to lazy", () => {
-      const element = renderComponent(
-        "alchemy-picture-thumbnail",
-        "<alchemy-picture-thumbnail></alchemy-picture-thumbnail>"
-      )
-      element.createImage("https://example.com/test.jpg")
-
-      expect(element.image.loading).toBe("lazy")
-    })
-
     it("uses default src from attribute", () => {
       const element = renderComponent(
         "alchemy-picture-thumbnail",