sched/proxy: Remove superfluous clear_task_blocked_in()

Per the discussion here:

  https://lore.kernel.org/all/20260403112810.GG3738786@noisy.programming.kicks-ass.net/

The reason for this condition is that the signal condition in
try_to_block_task() would set_task_blocked_in_waking(). However, it no longer
does that, in fact, that path does clear_task_blocked_on().

However, per the discussions here:

  https://lore.kernel.org/r/dc61cf77-e541-441d-a708-c40e19aa0db2%40amd.com
  https://lore.kernel.org/r//9dd1d24d-45d3-4ee2-8e67-8305b34bfb6d%40amd.com

there are a few other edge cases that needed this. But they're all
gone now, so remove the condition.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20260526113322.120970670%40infradead.org