Revert "oniro-image-base-tests: bump rootfs size to 2500M"

The rootfs size is no more affected by the debug mode, the reverted
commit has no purpose now.

This reverts commit 7a5149bc.

Signed-off-by: Davide Gardenal <davide.gardenal@huawei.com>

meta-oniro-core/recipes-core/images/oniro-image-base-tests.bb

@@ -19,5 +19,3 @@ EXTRA_IMAGE_FEATURES:append = " ptest-pkgs debug-tweaks"
 # For testing purposes, we want to have an extra ext4 format for the root
 # filesystem.
 IMAGE_FSTYPES:append = " ext4"
-
-ROOT_PARTITION_SIZE = "2500M"