[python] Remove special type handling in QueryCondition parser required for Python 3.7

[nguyenv]

https://github.com/single-cell-data/TileDB-SOMA/blob/main/apis/python/src/tiledbsoma/_query_condition.py#L374-L379

The Python AST module had a significant refactoring between 3.7 and 3.8 which in our code required special handling like in the example above. In 3.7, ast.Num, ast.Str, and ast.Bytes nodes needed to be handled separately. As of 3.8, that was deprecated and are now handled as ast.Constant or ast.NameConstant.

[johnkerl]

Related to #2181