Avoid overriding LSP_Uri '=' operator as abstract

This is no longer supported by the edge compiler, and we have
multiple implicit equality comparisons in our code.

Just add a comment warning the user that comparisons between
Virtual_File objects should be prefered instead.

For eng/shared/release#1774

Author: AnthonyLeonardoGracio

liblsp_3_16/source/lsp-types.ads

@@ -294,15 +294,15 @@ package LSP.Types is
    subtype ProgressToken is LSP_Number_Or_String;
 
    type LSP_URI is private;
+   --  Type for LSP URI.
+   --  Please avoind comparing URIs with "=": two URIs can point the same file
+   --  even when they are distinct. In most case we shouldn't compare URIs,
+   --  but find corresponding files using GNATCOLL.VFS and compare their
+   --  normalized names instead.
 
    function Equal (Left, Right : LSP_URI) return Boolean;
    --  Let's try to avoid URI comparison.
 
-   overriding function "=" (Left, Right : LSP_URI) return Boolean is abstract;
-   --  Disable URI comparison with "=". Two URIs can point the same file
-   --  even when they are distinct. In most case we shouldn't compare URIs,
-   --  but find corresponding files and compare their normalized names.
-
    function File_To_URI (File : String) return LSP.Types.LSP_URI;
    --  Turn the File name into an URI