tidy(installer): remove no-op --version CLI arg of installer

This wasn't used at all.

installer/lib/installer.py

@@ -119,7 +119,6 @@ class Installer:
         self,
         root: str = "~/invokeai",
         yes_to_all: bool = False,
-        version: Optional[str] = None,
         find_links: Optional[str] = None,
         wheel: Optional[Path] = None,
     ) -> None:

installer/lib/main.py

@@ -29,13 +29,6 @@ if __name__ == "__main__":
         default=False,
     )
 
-    parser.add_argument(
-        "--version",
-        dest="version",
-        help="Version of InvokeAI to install. Default to the latest stable release. A special 'pre' value will install the latest published pre-release version.",
-        default=None,
-    )
-
     parser.add_argument(
         "--find-links",
         dest="find_links",