Do not dump BOARD_VNDK_VERSION

Soong dumps BOARD_VNDK_VERSION to check if devices use VNDK when VNDK is
first introduced. However, VNDK is fully used from all device so this is
no longer required. Also, BOARD_VNDK_VERSION property is expected to be
deprecated along with VNDK deprecation. This change removes
BOARD_VNDK_VERSION from dump variable target.

Bug: 316829758
Test: AOSP CF build succeeded
Change-Id: I2fdb92a0e03629366a515d3b6705f7a7db0c1159