On the vehicle form, linked to your Schedule E, there are instructions for removing it. However, I suspect if you just delete the form you'll be fine--assuming you've always just taken a mileage allowance and any tolls or parking, etc. [The reason it's complicated is because the assumption is that you might be taking actual expenses including the depreciation of the car, and so then the sales price when you dispose of it might need to be recovered. Most people don't do this, especially for a rental, but it's the same form for everyone.]
BTW, it might not be much trouble. You know how far it is to the rental, and about when you've gone, so it's pretty easy to make up a record of those trips, which you keep with your other tax records in case the IRS ever asks. Regarding the mileage on the car, you can estimate that too if you need to, as all it will do is change the amount of personal miles, which doesn't affect your taxes. (I actually keep records of every trip, but that's because I also use my cars for my Schedule C business. I mark entries that are tax-related with a code, like M for medical, R for rental, B for business, C for nonprofit-related.)
Example: It's 8 miles roundtrip from my home to my rental, I went 6 times, I can show 48 miles on the rental. I describe the car as either the one I used the most or "various." If I'm using various, I put in 48000 (or something) to start, and 58000 to end the year, show all but 48 miles as personal (I don't commute and it doesn't matter, this is just to be sure you're not counting commuting miles as deductible!) This yields a deduction of about $25, which lowers tax (22% + 5% CO) about $7, payment for my time filling out the form I suppose. Hmmm, I can see why you might not want to bother!
