Revert "HHH-3192 - SchemaValidator column nullability check"

This reverts commit 3b8dc32.

Author: sebersole

hibernate-core/src/main/java/org/hibernate/tool/schema/internal/AbstractSchemaValidator.java

@@ -139,7 +139,6 @@ protected void validateTable(
 				);
 			}
 			validateColumnType( table, column, existingColumn, metadata, dialect );
-			validateColumnNullability( table, column, existingColumn );
 		}
 	}
 
@@ -165,22 +164,6 @@ protected void validateColumnType(
 		}
 	}
 
-	private void validateColumnNullability(Table table, Column column, ColumnInformation existingColumn) {
-		if ( existingColumn.getNullable() == Boolean.FALSE ) {
-			// the existing schema column is defined as not-nullable
-			if ( column.isNullable() ) {
-				// but it is mapped in the model as nullable
-				throw new SchemaManagementException(
-						String.format(
-								"Schema validation: column defined as not-null in the database, but nullable in model - [%s] in table [%s]",
-								column.getName(),
-								table.getQualifiedTableName()
-						)
-				);
-			}
-		}
-	}
-
 	protected void validateSequence(Sequence sequence, SequenceInformation sequenceInformation) {
 		if ( sequenceInformation == null ) {
 			throw new SchemaManagementException(