Revert "Per element schema parsing in ConvertToBeamRows (#36393)" (#36507)

This reverts commit 1a6ec3a.

Author: Abacn

sdks/python/apache_beam/io/gcp/bigquery.py

@@ -2764,9 +2764,6 @@ def expand(self, input):
 
   class ConvertToBeamRows(PTransform):
     def __init__(self, schema, dynamic_destinations):
-      if not isinstance(schema,
-                        (bigquery.TableSchema, bigquery.TableFieldSchema)):
-        schema = bigquery_tools.get_bq_tableschema(schema)
       self.schema = schema
       self.dynamic_destinations = dynamic_destinations