Avoid using accessSecretStorage to create 4S (#30244)

* remove resetCrossSigning flag, which is no longer in use

* drop unnecessary check for cross-signing

The only place where verifyUser is called already checks that cross-signing is
set up.  (The function name is also incorrect, since it checks for the
cross-signing key, and not for 4S.)

* avoid calling accessSecretStorage to set up cross-signing or 4S

Send the user to the Encryption settings tab instead

* only create secret storage when specifically asked to

* deprecate using accessSecretStorage to create new 4S

* also remove the obsolete snapshot

* add tests

* Tweak comment

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

---------

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

test/unit-tests/SecurityManager-test.ts

@@ -67,6 +67,17 @@ describe("SecurityManager", () => {
                     await accessSecretStorage(jest.fn());
                 }).rejects.toThrow("End-to-end encryption is disabled - unable to access secret storage");
             });
+
+            it("throws if there is no 4S", async () => {
+                // Given a client with no default 4S key ID
+                stubClient();
+
+                // When I run accessSecretStorage
+                // Then we throw an error
+                await expect(async () => {
+                    await accessSecretStorage(jest.fn());
+                }).rejects.toThrow("Secret storage has not been created yet");
+            });
         });
 
         it("should show CreateSecretStorageDialog if forceReset=true", async () => {