Revert "add: string slicing operator for jwt-role-claim-key"

This reverts commit fe0386e9c4.

As discussed in https://github.com/PostgREST/postgrest/pull/4984#issuecomment-4652725178.

docs/references/auth.rst

@@ -234,17 +234,6 @@ The DSL follows the `JSONPath <https://goessner.net/articles/JsonPath/>`_ expres
 - ``==^`` selects the first array element that ends with the right operand
 - ``*==`` selects the first array element that contains the right operand
 
-The selected role value can also be sliced using the slice operator ``[a:b]``. It is similar to `slice operator in python <https://docs.python.org/3/library/functions.html#slice>`_. Negative index values are also supported. The syntax is as:
-
-- ``[a:b]`` take slice from index ``a`` up to ``b``
-- ``[a:]`` take slice from index ``a`` to end
-- ``[:b]`` take slice from start to index ``b``
-- ``[:]`` select everything, no slicing
-
-.. important::
-
-  Make sure that you are not taking a slice where the start index comes after the end index like ``[11:2]``. The result of this would be empty string and so no role would get selected.
-
 Usage examples:
 
   .. code:: bash
@@ -266,11 +255,6 @@ Usage examples:
     jwt-role-claim-key = ".postgrest.roles[?(@ ==^ \"hor\")]"
     jwt-role-claim-key = ".postgrest.roles[?(@ *== \"utho\")]"
 
-    # {"postgrest":{"wlcg": ["/groupa", "/groupb/"]}}
-    # skip the "/" character using slice operator
-    jwt-role-claim-key = ".postgrest.wlcg[0][1:]"
-    jwt-role-claim-key = ".postgrest.wlcg[1][1:-1]"
-
 .. note::
 
   The string comparison operators are implemented as a custom extension to the JSPath and does not strictly follow the `RFC 9535 <https://www.rfc-editor.org/rfc/rfc9535.html>`_.