Move column dropping to DB functions

[mathemancer]

Related to #2737

• Removes SQLAlchemy from db.columns.operations.drop
• Removes SQLAlchemy from db.columns.operations.alter.batch_alter_table_drop_columns
• Fixes a bug in the psycopg2_conn function execution wrapper.
• On top of functions added to support the above, adds a DB function to get the correct casting function name from any type.

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• I added or updated documentation (if applicable).
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  visible errors.

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[Anish9901]

Unassigning myself as @dmos62 has already reviewed the PR.

[dmos62]

I appreciate the naming changes!

[dmos62]

Appreciated 👍

[dmos62]

Naming looks great!