[Test][BugFix] Remove invalid finegrained_tp_config from Kimi-K2.6 test config (#15065)

### What this PR does / why we need it?

This PR removes the invalid `\"finegrained_tp_config\":
{\"lmhead_tensor_parallel_size\":16}` from the decode node's additional
configuration in `Kimi-K2.6-W4A8-64k-1k-TPOT50-PD.yaml`. The decode node
is configured with `tp_size: 4`, so setting
`lmhead_tensor_parallel_size` to 16 is invalid and causes configuration
mismatches.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Nightly multi-node end-to-end tests.

Signed-off-by: wangzhishenghw <wangzhisheng6@h-partners.com>