Only assert-max-image-size for static partitions.

assert-max-image-size doesn't make sense for
dynamic partitions, as build_image.py always find the
right size for the output image. Hence:

- build_image.py no longer need to write generated_*_info.txt
  (which contains the size of the image).
- assert-max-image-size on the static BOARD_*IMAGE_PARTITION_SIZE. If
  a partition is dynamic, that variable isn't set, and
  assert-max-image-size becomes a no-op. If the partition is static,
  assert-max-image-size checks the static partition size as it used
  to be.
- Fix read-size-of-partitions to use the size of the partition by
  reading the image directly (instead of using generated_*_info.txt).

For devices without AVB, with DAP enabled, and does not have
RESERVED_SIZE for partitions, because of right sizing, the original
code always warns about approaching size limits. Since such checks
doesn't make sense for dynamic partitions, remove them.

Test: builds on device with dynamic partitions
Test: builds on cuttlefish with DAP enabled (without AVB), no
      more size limit warnings:
WARNING: out/target/product/vsoc_x86/vendor.img approaching size limit (X now; limit X)

Fixes: 122377935
Change-Id: I75e1b8322197cb18cf397d02aefd49d777bb6405