I don't know what this shield looks like, but I'm going to guess that the battery is removable/replaceable. Is that the case?
Did it come with a battery, or was it up to you to provide it?
The DS1307 has a little quirk in that it requires that Vbat be grounded when there is no backup battery connected. R5 is meant to pull Vbat down to ground in the absence of a backup battery. Without that resistor, the DS1307 would not function correctly if one were to try and use it without a battery installed and powered via the ESP mainboard/VCC.
From the DS1307's data sheet:
If a backup supply is not required, VBAT must be grounded.
Now, is it a good solution to this requirement? ...Not really. For a 48mAh 3V cell, this will reduce the best possible backup time to 3 years, and the drain will occur even when the DS1307 is running off VCC.
However, I can definitely understand their reasoning. It's a shield, it is aimed at a fairly wide audience and they probably just made the decision that it would be better if the DS1307 worked in every possible usage case rather than keep time for a decade.
That said, as long as you aren't planning on using it without a backup battery installed, you can simply remove it and eliminate that source of drain on the battery.