ota_from_target_files: remove duplicate setting of recovery_img

This variable is already set earlier in the script and does not need
to be wrapped inside of the if statement

Change-Id: I91b7f7d2fc911a3910b3df09cff0ca0f44fe7741
releasetools: Fix error text in ota_from_target_files

property isn't the variable name, prop is

Change-Id: I0fc6adddfd51ba9bc79f6559c61cd831203c9e3d