This scheme was used for reducing memory usage when vmagent runs on a machine with big number of CPU cores
and the ingestion rate isn't too big. The scheme with channel-based pool could reduce memory usage,
since it minimizes the number of PushCtx structs in the pool in this case.
Performance tests didn't reveal significant difference in memory usage under both low and high ingestion rate
between plain sync.Pool and the current hybrid scheme, so replace the scheme with plain sync.Pool in order
to simplify the code.