Remove inconsistent validation for TimeDimensionParameter (#1314)

Two things:
- This error wasn't do what it was supposed to do, since it never
checked if `date_part` was passed. I don't think this ever got triggered
because MFS was parsing the grain from the `name` param and passing it
via the `grain` param instead.
- I ran into this error in the process of trying to create consistency
in the behavior of our Jinja params. Since most interfaces allow passing
grain via dundered syntax, this interface is inconsistent. If we
eventually want to retire the dunder syntax, we should deprecate it
everywhere at once to avoid creating confusion for our users in the
meantime.

metricflow-semantics/metricflow_semantics/specs/query_param_implementations.py

@@ -41,11 +41,6 @@ def _implements_protocol(self) -> TimeDimensionQueryParameter:
     grain: Optional[TimeGranularity] = None
     date_part: Optional[DatePart] = None
 
-    def __post_init__(self) -> None:  # noqa: D105
-        parsed_name = StructuredLinkableSpecName.from_name(self.name)
-        if parsed_name.time_granularity:
-            raise ValueError("Must use object syntax for `grain` parameter if `date_part` is requested.")
-
     @property
     def query_resolver_input(self) -> ResolverInputForGroupByItem:  # noqa: D102
         fields_to_compare = [