DEV: Remove Discourse.redis.delete_prefixed (#22103)

This method is a huge footgun in production, since it calls
the Redis KEYS command. From the Redis documentation at
https://redis.io/commands/keys/:

> Warning: consider KEYS as a command that should only be used in
production environments with extreme care. It may ruin performance when
it is executed against large databases. This command is intended for
debugging and special operations, such as changing your keyspace layout.
Don't use KEYS in your regular application code.

Since we were only using `delete_prefixed` in specs (now that we
removed the usage in production in 24ec06ff85)
we can remove this and instead rely on `use_redis_snapshotting` on the
particular tests that need this kind of clearing functionality.

spec/requests/session_controller_spec.rb

@@ -2350,10 +2350,12 @@ RSpec.describe SessionController do
     end
 
     context "when rate limited" do
+      before { RateLimiter.enable }
+
+      use_redis_snapshotting
+
       it "rate limits login" do
         SiteSetting.max_logins_per_ip_per_hour = 2
-        RateLimiter.enable
-        RateLimiter.clear_all!
         EmailToken.confirm(email_token.token)
 
         2.times do
@@ -2371,9 +2373,6 @@ RSpec.describe SessionController do
       end
 
       it "rate limits second factor attempts by IP" do
-        RateLimiter.enable
-        RateLimiter.clear_all!
-
         6.times do |x|
           post "/session.json",
                params: {
@@ -2400,8 +2399,6 @@ RSpec.describe SessionController do
       end
 
       it "rate limits second factor attempts by login" do
-        RateLimiter.enable
-        RateLimiter.clear_all!
         EmailToken.confirm(email_token.token)
 
         6.times do |x|
@@ -2644,44 +2641,47 @@ RSpec.describe SessionController do
       )
     end
 
-    it "should correctly rate limits" do
-      RateLimiter.enable
-      RateLimiter.clear_all!
+    describe "rate limiting" do
+      before { RateLimiter.enable }
 
-      user = Fabricate(:user)
+      use_redis_snapshotting
+
+      it "should correctly rate limits" do
+        user = Fabricate(:user)
+
+        3.times do
+          post "/session/forgot_password.json", params: { login: user.username }
+          expect(response.status).to eq(200)
+          expect(response.parsed_body["error"]).not_to be_present
+        end
 
-      3.times do
         post "/session/forgot_password.json", params: { login: user.username }
-        expect(response.status).to eq(200)
-        expect(response.parsed_body["error"]).not_to be_present
-      end
+        expect(response.status).to eq(422)
 
-      post "/session/forgot_password.json", params: { login: user.username }
-      expect(response.status).to eq(422)
+        3.times do
+          post "/session/forgot_password.json",
+               params: {
+                 login: user.username,
+               },
+               headers: {
+                 "REMOTE_ADDR" => "10.1.1.1",
+               }
+
+          expect(response.status).to eq(200)
+          expect(response.parsed_body["error"]).not_to be_present
+        end
 
-      3.times do
         post "/session/forgot_password.json",
              params: {
                login: user.username,
              },
              headers: {
-               "REMOTE_ADDR" => "10.1.1.1",
+               "REMOTE_ADDR" => "100.1.1.1",
              }
 
-        expect(response.status).to eq(200)
-        expect(response.parsed_body["error"]).not_to be_present
+        # not allowed, max 6 a day
+        expect(response.status).to eq(422)
       end
-
-      post "/session/forgot_password.json",
-           params: {
-             login: user.username,
-           },
-           headers: {
-             "REMOTE_ADDR" => "100.1.1.1",
-           }
-
-      # not allowed, max 6 a day
-      expect(response.status).to eq(422)
     end
 
     context "for a non existant username" do