remove customPQConfig

[pavoljuhas]

Consider removing support for customPQConfig. Check if it can be improved so there are no Python calls and GIL / threading issues in diffpy.srreal when parallelizing over threads.

[pavoljuhas]

Deprecated in version 1.4.0.

TODO

• remove it in next major release
• deprecate NoMetaStructureAdapter class and convert nometa() to no-op