Fix T101706: Specify the correct UI location for Images as Planes addon

As part of a change years ago[1], the addon location was moved from the
`Add->Mesh` menu to the `Add->Image` menu but the "location" field was
never updated.  The manual is already correct.

[1] 07b8375e

io_import_images_as_planes.py

@@ -5,7 +5,7 @@ bl_info = {
     "author": "Florian Meyer (tstscr), mont29, matali, Ted Schundler (SpkyElctrc), mrbimax",
     "version": (3, 5, 0),
     "blender": (2, 91, 0),
-    "location": "File > Import > Images as Planes or Add > Mesh > Images as Planes",
+    "location": "File > Import > Images as Planes or Add > Image > Images as Planes",
     "description": "Imports images and creates planes with the appropriate aspect ratio. "
                    "The images are mapped to the planes.",
     "warning": "",