Docs: Update the IModuleManager and IOwnerManager interfaces to clarify the usage of the prevModule and prevOwner (#993)

Updated the `IModuleManager` and `IOwnerManager` interfaces to clarify
the usage of the `prevModule` and `prevOwner` parameters in the
`disableModule` and `removeOwner` functions. Added details specifying
that when the module or owner to be removed is the first (or only)
element in the list, the respective `prevModule` or `prevOwner` must be
set to the sentinel address `0x1`. This improves understanding of the
linked list structure used in these functions.

fixes #992

---------

Co-authored-by: Nicholas Rodrigues Lordello <n@lordello.net>
Co-authored-by: Shebin John <admin@remedcu.com>

Author: 3 people

contracts/interfaces/IModuleManager.sol

@@ -27,7 +27,10 @@ interface IModuleManager {
     /**
      * @notice Disables the module `module` for the Safe.
      * @dev This can only be done via a Safe transaction.
-     * @param prevModule Previous module in the modules linked list.
+     * @param prevModule Previous module in the modules linked list. If the module to be
+     *        disabled is the first (or only) element of the list, `prevModule` MUST be
+     *        set to the sentinel address `0x1` (referred to as `SENTINEL_MODULES` in the
+     *        implementation).
      * @param module Module to be removed.
      */
     function disableModule(address prevModule, address module) external;

contracts/interfaces/IOwnerManager.sol

@@ -21,7 +21,10 @@ interface IOwnerManager {
     /**
      * @notice Removes the owner `owner` from the Safe and updates the threshold to `_threshold`.
      * @dev This can only be done via a Safe transaction.
-     * @param prevOwner Owner that pointed to the owner to be removed in the linked list
+     * @param prevOwner Owner that pointed to the `owner` to be removed in the linked list.
+     *        If the owner to be removed is the first (or only) element of the list,
+     *        `prevOwner` MUST be set to the sentinel address `0x1` (referred to as
+     *        `SENTINEL_OWNERS` in the implementation).
      * @param owner Owner address to be removed.
      * @param _threshold New threshold.
      */
@@ -30,7 +33,10 @@ interface IOwnerManager {
     /**
      * @notice Replaces the owner `oldOwner` in the Safe with `newOwner`.
      * @dev This can only be done via a Safe transaction.
-     * @param prevOwner Owner that pointed to the owner to be replaced in the linked list
+     * @param prevOwner Owner that pointed to the `oldOwner` to be replaced in the linked list.
+     *        If the owner to be replaced is the first (or only) element of the list,
+     *        `prevOwner` MUST be set to the sentinel address `0x1` (referred to as
+     *        `SENTINEL_OWNERS` in the implementation).
      * @param oldOwner Owner address to be replaced.
      * @param newOwner New owner address.
      */