applypatch: Drop the support for patching non-EMMC targets.

Patching regular files is used in file-based OTA only, which has become
obsolete.

Bug: 35853185
Test: Apply an incremental that patches the boot.img.
Test: /system/bin/install-recovery.sh works.
Test: recovery_component_test passes.
Change-Id: Id44e42c4bc63f2162ecc8a6df1cb528b7ae6b0a9