[SPARK-18901][ML] Require in LR LogisticAggregator is redundant

## What changes were proposed in this pull request?

In MultivariateOnlineSummarizer,

`add` and `merge` have check for weights and feature sizes. The checks in LR are redundant, which are removed from this PR.

## How was this patch tested?

Existing tests.

Author: wm624@hotmail.com <wm624@hotmail.com>

Closes #17478 from wangmiao1981/logit.