No evidence whatsoever that Trump was ever likely to be removed prior to the strike.
No evidence whatsoever that the strike has in any meaningful way impacted impeachment proceedings.
No evidence whatsoever in favor of this particular conspiracy theory.
One important consideration that your assessment leaves out is; what was Trump thinking?
There were plenty of signs that he was (and still is) extremely concerned about being impeached. Seems that the most obvious answer for his assassination of Soleimani was a combination of a pathological need to lash out coupled with a long-standing strategic mini-plan to have a few easy to implement, dramatic “protect the nation against the bad guys” cans of whupass on the shelf for emergencies.
My leading “conspiracy theory” is that The Impetuous One indulged in a can of whupass to try and make himself feel better.
Only a naive intellectual would expect Trump’s actions to have any rational origins.