Update: If you really care about the number of files in /boot, I suggest you read this post, which will allow you to remove emmc_autoscript as well.

Only the following files are kept:

# find
.
./System.map-4.19.6-aml-s9xxx
./uEnv.ini
./config-4.19.6-aml-s9xxx
./dtb
./dtb/meson-gxl-s905d-phicomm-n1.dtb
./emmc_autoscript
./emmc_autoscript.cmd
./uInitrd
./zImage

But in fact, this is still not a minimal file list. System.map-4.19.6-aml-s9xxx, config-4.19.6-aml-s9xxx, emmc_autoscript.cmd are also not needed for N1 to boot. That is, the minimal list would be:

# find
.
./uEnv.ini
./dtb
./dtb/meson-gxl-s905d-phicomm-n1.dtb
./emmc_autoscript
./uInitrd
./zImage

I tested this configuration, it worked. But for debugging purpose, those three files are kept on my box.