fix(sql): remove dead code from sql_trigger_begin

NO_DOC=internal
NO_TEST=internal
NO_CHANGELOG=internal

The following commit introduced a tautological if expression:

```gitcommit
sql: introduce structs assembling DDL arguments during parsing (ba56b145fafaa3)
```

Due to the changes in commit

```gitcommit
sql: refactor memory allocation system (cb777136dd7a0c)
```

the allocations in sql expressions became infallible, which means
that we may safely fix static analysis warnings by dropping the
tautological comparison altogether.

Original patch by Feodor Alexandrov.