sql: do not hard code the LIMIT clause in the table_info section (#1563)

Seeing a lot of issues in Discord in which the LLM is not using the
correct LIMIT clause for different SQL dialects. ie, it's using `LIMIT`
for mssql instead of `TOP`, or instead of `ROWNUM` for Oracle, etc.
I think this could be due to us specifying the LIMIT statement in the
example rows portion of `table_info`. So the LLM is seeing the `LIMIT`
statement used in the prompt.
Since we can't specify each dialect's method here, I think it's fine to
just replace the `SELECT... LIMIT 3;` statement with `3 rows from
table_name table:`, and wrap everything in a block comment directly
following the `CREATE` statement. The Rajkumar et al paper wrapped the
example rows and `SELECT` statement in a block comment as well anyway.
Thoughts @fpingham?

tests/unit_tests/test_sql_database_schema.py

@@ -54,9 +54,10 @@ def test_table_info() -> None:
         user_name VARCHAR NOT NULL, 
         PRIMARY KEY (user_id)
     )
-
-    SELECT * FROM 'user' LIMIT 3;
+    /*
+    3 rows from user table:
     user_id user_name
+    */
     """
 
     assert sorted(" ".join(output.split())) == sorted(" ".join(expected_output.split()))