### What changes were proposed in this pull request?
1, compute summary and update distributions in one pass;
2, remove logic related to check `shouldDistributeGaussians`
### Why are the changes needed?
In current impl, GMM need to trigger two jobs at one iteration:
1, one to compute summary;
2, if `shouldDistributeGaussians = ((k - 1.0) / k) * numFeatures > 25.0`, trigger another to update distributions;
`shouldDistributeGaussians` is almost true in practice, since numFeatures is likely to be greater than 25.
We can use only one job to impl above computation, by following the logic in `KMeans`: using `reduceByKey` to compute statistics for each center
### Does this PR introduce any user-facing change?
No
### How was this patch tested?
existing testsuites
Closes#27784 from zhengruifeng/gmm_avoid_distri_gaussian.
Authored-by: zhengruifeng <ruifengz@foxmail.com>
Signed-off-by: zhengruifeng <ruifengz@foxmail.com>
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