Remove unused sequence_name in sql_for_insert

All adapters (sqlite3, mysql2, postgresql, oracle-enhanced, sqlserver)
doesn't use `sequence_name` in `sql_for_insert`.

https://github.com/rsim/oracle-enhanced/blob/4e0db270a93859c9713fd079dbb315b9fe550e57/lib/active_record/connection_adapters/oracle_enhanced/database_statements.rb#L79-L85
https://github.com/rails-sqlserver/activerecord-sqlserver-adapter/blob/959fe8f49744460b876bc205c73259f8d4f37629/lib/active_record/connection_adapters/sqlserver/database_statements.rb#L226-L249

It can be handled in `exec_insert` like postgresql adapter if we want.

Author: kamipo

activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb

@@ -131,7 +131,7 @@ def exec_query(sql, name = "SQL", binds = [], prepare: false)
       # +binds+ as the bind substitutes. +name+ is logged along with
       # the executed +sql+ statement.
       def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil)
-        sql, binds = sql_for_insert(sql, pk, sequence_name, binds)
+        sql, binds = sql_for_insert(sql, pk, binds)
         exec_query(sql, name, binds)
       end
 
@@ -487,7 +487,7 @@ def select_prepared(sql, name = nil, binds = [])
           exec_query(sql, name, binds, prepare: true)
         end
 
-        def sql_for_insert(sql, pk, sequence_name, binds)
+        def sql_for_insert(sql, pk, binds)
           [sql, binds]
         end
 

activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb

@@ -110,7 +110,7 @@ def exec_delete(sql, name = nil, binds = [])
         end
         alias :exec_update :exec_delete
 
-        def sql_for_insert(sql, pk, sequence_name, binds) # :nodoc:
+        def sql_for_insert(sql, pk, binds) # :nodoc:
           if pk.nil?
             # Extract the table from the insert sql. Yuck.
             table_ref = extract_table_ref_from_insert_sql(sql)