Omit GenericModel docstring from generated types

[phillipdupuis]

With new installations, it seems that if you convert a generic model the resulting .ts definitions have this docstring above all models subclassing pydantic's GenericModel:

/**
 * Abstract base class for generic types.
 *
 * A generic type is typically declared by inheriting from
 * this class parameterized with one or more type variables.
 * For example, a generic mapping type might be defined as::
 *
 *   class Mapping(Generic[KT, VT]):
 *       def __getitem__(self, key: KT) -> VT:
 *           ...
 *       # Etc.
 *
 * This class can then be used as follows::
 *
 *   def lookup_name(mapping: Mapping[KT, VT], key: KT, default: VT) -> VT:
 *       try:
 *           return mapping[key]
 *       except KeyError:
 *           return default
 */

(and it's obviously useless, so it should be removed by default)