Fix deprecated API usages

[mguenther]

We currently have two sources of deprecated API usages that we should address as soon as possible. Violations are:

• DefaultRecordConsumer should call poll(Duration) instead of poll(long)
• EmbeddedConnectConfig: Remove INTERNAL_KEY_CONVERTER_CLASS_CONFIG
• EmbeddedConnectConfig: Remove INTERNAL_VALUE_CONVERTER_CLASS_CONFIG
• EmbeddedConnectConfigTest: Remove INTERNAL_KEY_CONVERTER_CLASS_CONFIG
• EmbeddedConnectConfigTest: Remove INTERNAL_VALUE_CONVERTER_CLASS_CONFIG

[mguenther]

Fixed the deprecation on EmbeddedConnectConfig and EmbeddedConnectConfigTest.

Won't fix for now for DefaultRecordConsumer. We rely on the metadata updates to provide seek-semantics for our adhoc consumer. Since the API documentation of kafka-clients only marks the poll(long) method as deprecated, but does not say that it is going to be removed (KIP-266 does neither), we'll keep this as it is for now. The reason is that using poll(Duration) would overly complicate the code of the adhoc consumer, since we'd have to wait until we get the first assignments and handle potentially received records as well. We'll fix this if we really have to, but for now, the probable issue of blocking on metadata updates seems fine to me in the context of integration tests.