fix a deadlock in the consumer mock

[moonpolysoft]

Found a deadlock in the MockAutoPartitionConsumer. The Close() function does all of its work from within a sync.Once. However, the AsyncClose() function utilizes the same sync.Once to do its work. Close() calls AsyncClose() from within the once invocation and results in a deadlock as the mutex is being held by the outer Close().

This change inlines the operations AsyncClose() would've performed into the main body of Close(), removing the possibility for deadlock.

[frairon]

Good catch, thanks a lot @moonpolysoft !