Remove legacy `publicKey` and `privateKey` property from `UserDto`

[SailReal]

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• I have searched existing issues for duplicates
• I agree to follow this project's Code of Conduct

Summary

When we release a new major release, we drop these properties to simplify and reduce the size of the response.

Motivation

See summary.

hub/backend/src/main/java/org/cryptomator/hub/api/UserDto.java

Lines 30 to 36 in afc7a17

	// Accept either "ecdhPublicKey" or the legacy "publicKey" on input
	@Nullable @JsonProperty("ecdhPublicKey") @OnlyBase64Chars String ecdhPublicKey,
	@Nullable @JsonProperty("publicKey") @OnlyBase64Chars String publicKey,
	@Nullable @JsonProperty("ecdsaPublicKey") @OnlyBase64Chars String ecdsaPublicKey,
	// Accept either "privateKeys" or the legacy "privateKey" on input
	@Nullable @JsonProperty("privateKeys") @ValidJWE String privateKeys,
	@Nullable @JsonProperty("privateKey") @ValidJWE String privateKey,

Considered Alternatives

No response

Anything else?

No response