`datafusion-examples` should only use the `datafusion` crate

[nuno-faria]

datafusion-examples currently uses subcrates like datafusion-expr:

datafusion/datafusion-examples/Cargo.toml

Lines 54 to 57 in 0576a0b

	datafusion-expr = { workspace = true }
	datafusion-physical-expr-adapter = { workspace = true }
	datafusion-proto = { workspace = true, features = ["parquet"] }
	datafusion-sql = { workspace = true }

Since the datafusion crate already exports most these, it should be preferred in the examples. Here's @alamb original reasoning: #14305

The fix is easy to automate. However, we should also add a CI check to prevent these subcrates to be unnecessarily added in the future.

[alamb]

💯 agree