Disable relocation_packer and migrate to SHT_RELR sections.

Proposal for adding SHT_RELR sections in the generic-abi is at
https://groups.google.com/forum/#!topic/generic-abi/bX460iggiKg

Comparison with relocation_packer for aosp_marlin-userdebug:
$ du -B1 -s */out/target/product/marlin/system
 996958208      base/out/target/product/marlin/system
1008340992      no_pack/out/target/product/marlin/system
 997801984      sht_relr/out/target/product/marlin/system

base contains a build with current settings.
no_pack contains a build with relocation_packer disabled.
sht_relr contains a build with SHT_RELR sections enabled.

relocation_packer was saving 11,382,784 bytes (no_pack - base).
SHT_RELR sections are saving 10,539,008 bytes (no_pack - sht_relr).

Bug: None
Test: Built aosp_marlin-userdebug image, boots on device.
Test: Built aosp_x86_64-userdebug image, boots in emulator.
Change-Id: I448dc95baa4976b68ce2659b80498539426775f9