The supervisor of telegrams at the War Department was so appalled at the defiant tone of McClellan's message and the extraordinary charge against the government that he directed his staff to strike the words before relaying it to Edwin Stanton. Source
Bonus: Quote was in original telegraph from McClellen to Stanton regarding his loss at Gaines Mill, but the Telegraph Supervisor in the War Dept. directed his staff to remove these sentences before relaying to Stanton.
When Little Mac's message reached the War Department, Major Johnson sent for Sanford, who at once said that the charge made by McClellan was false, and that he, as military supervisor of telegrams, would not allow it to go before the Secretary of War. He then directed the despatch to be recopied, omitting the trivia questions lines, and the revised copy was delivered to Stanton.
There is a 2016 thread on this subject, A bit too f a debate if Stanton and Lincoln ever saw those two sentences.
But I believe the question's answer intent surrounds those lines being vetted from the original document.
Just spent the last hour reading on this subject and there is no agreement on who vetted those lines.
Hi All ("If I save this army now, I tell you plainly that I owe no thanks to you or to any other persons in Washington. You have done your best to sacrifice this army.") In various books and places I've read of these two infamous lines at the end of McClellan's telegram to DC after the Battle...
Colonel Everett Peabody
Edward S. Sanford, Head of the War Department Telegraph, felt this remark was too flammatory and removed it from the message before passing the telegram on to Edward Stanton, Secretary of War. Stanton and Lincoln did not know of this excerpt till later.
Bonus: The two sentences in question from McClellan's letter to Secretary of War, Edward Stanton were deleted from the telegram by Colonel Edward Sanford, a War Department telegrapher after receiving the telegram in Washington.
Everett Peabody (13 June 1830 – 6 April 1862) Source
BONUS: The last two sentences of McClellan's telegram were deleted by the War Department's telegraphic operator before the message was forwarded to Secretary of War Stanton. Neither Stanton or Lincoln received those two sentences as part of McClellan's telegram. Source
Edit - Note that the bonus question did not ask who wrote the sentences, nor did it ask to whom the message that included those sentences was intended to be delivered. As long as players mentioned the fact that the sentences were deleted by someone in the telegraph office, they were given credit for a correct answer.