Remove assorted deprecated APIs that are past the API health policy

[alamb]

Is your feature request related to a problem or challenge?

The API health policy deprecation guidelines say deprecated APIs remain for

6 major versions or 6 months, whichever is longer

main is at 55.0.0, so the next release is 56.0.0 and anything deprecated in 50.0.0 or earlier can now be removed.

These eight are independent one-offs, each a few lines in a different crate:

Item	Deprecated in	Replacement
ScalarValue::raw_data	46.0.0	to_array
get_statistics_with_limit	47.0.0	get_files_with_limit and compute_all_files_statistics
DisplayableExecutionPlan::to_stringified	47.0.0	indent or tree_render
ExprSimplifier::simplify_with_cycle_count	48.0.0	simplify_with_cycle_count_transformed
DynEq / DynHash re-export	50.0.0	datafusion_expr_common::dyn_eq
ExecutionProps::start_execution	50.0.0	mark_start_execution
UserDefinedFunctionPlanner	50.0.0	UnicodeFunctionPlanner and DateTimeFunctionPlanner
Now::new	50.2.0	new_with_config

Describe the solution you'd like

Remove all eight items and supporting code

These are independent, so this can be done as one PR or several -- feel free to pick off whichever items you like.

• While this is a breaking Rust API change, the PR should carry the api change label
• DO NOT add a note to the 56.0.0 upgrade guide, as removing deprecated APIs is clear and the compiler has guided people off them in the past

Describe alternatives you've considered

N/A

Additional context

Follow on to #23080, which did the same sweep at the 49.0.0 cutoff, and #24535.