releasetools: Remove recovery build remnants

This breaks "classic" (not blockmode) OTA ZIP generation

Generating recovery patches was originally removed in 84a770ad

5.0 added some additional related stuff - remove those remnants.

Change-Id: Idfb5540bd0c77b0cf69ac4290753fffc0c17f733
build: Don't use block mode by default, allow it to be chosen

Currently this uses the same logic as backuptool (but inverted)

i.e. block mode will be disabled in all cases where backuptool is enabled
which is the current default for all Omni builds.

Block mode is not needed now, and may never be needed for custom projects,
as block mode is preparation for dm-verity, which is mostly pointless on
devices with unlocked bootloaders since the kernel already has broken
the chain of trust.

TODO:  Determine if Nexus 9 *requires* blockmode.  If it does, this
may need to be reworked to allow the device to specify blockmode.

Change-Id: I36725b44f4066a43ec7e1615bd4b072f7eb3db28
build: Don't create recovery patch

Change-Id: I00a9ca268ed3f326a0fa5a913bc112ec8b290550