Remove unused sequence

No idea who made it.

db/migrate/20210211213304_drop_extra_sequence.rb

@@ -0,0 +1,9 @@
+class DropExtraSequence < ActiveRecord::Migration[6.1]
+  def up
+    execute 'DROP SEQUENCE IF EXISTS posts_id_seq2'
+  end
+
+  def down
+    # nothing to do here
+  end
+end

db/structure.sql

@@ -1233,18 +1233,6 @@ CREATE SEQUENCE public.post_votes_id_seq
 ALTER SEQUENCE public.post_votes_id_seq OWNED BY public.post_votes.id;
 
 
---
--- Name: posts_id_seq2; Type: SEQUENCE; Schema: public; Owner: -
---
-
-CREATE SEQUENCE public.posts_id_seq2
-    START WITH 7168
-    INCREMENT BY 1
-    NO MINVALUE
-    NO MAXVALUE
-    CACHE 1;
-
-
 --
 -- Name: posts_tags; Type: TABLE; Schema: public; Owner: -
 --
@@ -3408,6 +3396,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20191110172526'),
 ('20200908180652'),
 ('20201103140508'),
+('20210211213304'),
 ('21'),
 ('22'),
 ('23'),