I like Crazy Cat's answer and advise you to stop thinking in terms of what you will use, and instead think in terms of answering the questions on the form itself. Unless it is your intention to quite the second job, then it is part of your current income. It might work to ignore it, but if it's part of your ongoing life, why play games. A current pay stub from either or both jobs is fine, without an employment letter, but the stub is actually better evidence than the letter.
Further, it serves no purpose to provide things not required, like more than the one tax return transcript. The form asks for information from three forms, but only one return. Six months of pay stubs is an artifact from more than twenty years ago. One current one from each job, that shows current gross, the frequency of paydays, and year to date income, is plenty.