Unset BOARD_EXT4_SHARE_DUP_BLOCKS

* This allows us to remount ext4 partitions read-write
  on devices with dynamic partitions.

This reverts the following commits:

Revert "Move BOARD_EXT4_SHARE_DUP_BLOCKS to BoardConfigMainlineCommon.mk"

This reverts commit I0eb035ba6edf44719d5de4f09fd97b5783537597.

Revert "enable BOARD_EXT4_SHARE_DUP_BLOCKS for generic_arm64"

This reverts commit 125b6d6e.

Change-Id: I3768374d6da59f969ea44c1965f75c934edf3b57