chore: drop redundant indexes in sqlite migration

store/migration/sqlite/0.26/02__drop_indexes.sql

+DROP INDEX IF EXISTS idx_user_username;
+DROP INDEX IF EXISTS idx_memo_creator_id;
+DROP INDEX IF EXISTS idx_attachment_creator_id;
+DROP INDEX IF EXISTS idx_attachment_memo_id;

store/migration/sqlite/LATEST.sql

@@ -21,8 +21,6 @@ CREATE TABLE user (
   description TEXT NOT NULL DEFAULT ''
 );
 
-CREATE INDEX idx_user_username ON user (username);
-
 -- user_setting
 CREATE TABLE user_setting (
   user_id INTEGER NOT NULL,
@@ -45,8 +43,6 @@ CREATE TABLE memo (
   payload TEXT NOT NULL DEFAULT '{}'
 );
 
-CREATE INDEX idx_memo_creator_id ON memo (creator_id);
-
 -- memo_relation
 CREATE TABLE memo_relation (
   memo_id INTEGER NOT NULL,
@@ -72,10 +68,6 @@ CREATE TABLE attachment (
   payload TEXT NOT NULL DEFAULT '{}'
 );
 
-CREATE INDEX idx_attachment_creator_id ON attachment (creator_id);
-
-CREATE INDEX idx_attachment_memo_id ON attachment (memo_id);
-
 -- activity
 CREATE TABLE activity (
   id INTEGER PRIMARY KEY AUTOINCREMENT,