sql: remove redundant type derivation from QP

Before value to be scanned in index search is passed to the iterator, it
is subjected to implicit type casting (which is implemented by
OP_ApplyType). If value can't be converted to required type,
user-friendly message is raised. Without this cast, type of iterator may
not match with type of key which in turn results in unexpected error.
However, array of types which is used to provide type conversions is
different from types of indexed fields: it is  modified depending on
types of comparison's operands. For instance, when boolean field is
compared with blob value, resulting type is assumed to be scalar. In
turn, conversion to scalar is no-op.  As a result, value with MP_BIN
format is passed to the iterator over boolean field.  To fix that let's
remove this transformation of types. Moreover, it seems to be redundant.

Part of #4187