Roll back un-necessary faiss change

[cydrain]

No description provided.

[cydrain]

/assign

[cydrain]

related PR: milvus-io/milvus#3015

[cydrain]

In Milvus 1.x, we did some enhancement in flat search.
From above code piece, we can see that it uses a complicated logic to decide to do parallel on nx or ny.
But in Milvus 2.x, knowhere uses folly to do parallel:

It makes 'nx' is always equal to 1, and omp_get_max_threads() always returns 1.
So there is no difference between do parallel on nx or ny.

So we can remove these APIs:

• exhaustive_L2sqr_IP_seq()
• exhaustive_L2sqr_IP_seq_on_nx()
• exhaustive_L2sqr_IP_seq_on_ny()

[cydrain]

/close

[sre-ci-robot]

@cydrain: Closing this issue.

In response to this:

/close

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