Replace malloc_not_svelte with malloc_low_memory.

The malloc_not_svelte variable name is confusing and makes the
low memory config the default. Change this so that the default is
the regular allocator, and that Malloc_low_memory is used to enable
the low memory allocator.

Update blueprint rules so that scudo is the default action.

Test: Verified scudo config is used by default.
Test: Verfified Android GO config uses the jemalloc low memory config.
Change-Id: Ie7b4b005a6377e2a031bbae979d66b50c8b3bcdb