remove StorageCredentials::BearerToken

[cataggar]

With this adding support for the azure-identity crate, we can probably remove the bearer token methods, as azure-identity is a significantly better mechanism for managing bearer tokens.
#757 (review)

azure-sdk-for-rust/sdk/storage/src/core/clients/storage_client.rs

Lines 31 to 36 in 66abb84

	pub enum StorageCredentials {
	Key(String, String),
	SASToken(Vec<(String, String)>),
	BearerToken(String),
	TokenCredential(Arc<dyn TokenCredential>),
	}

[github-actions]

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