Improve VM and OOM settings for erasing memory
_Originally created by @intrigeri on [#10487 (Redmine)](https://public-redmine-archive.tails.boum.org/code/issues/10487)_
The test suite in `feature/jessie` has good reasons to set
`oom_kill_allocating_task` to 0, and `/proc/sys/vm/overcommit_memory` to
0. These reasons probably apply as-is to
`local-includes/usr/share/initramfs-tools/scripts/init-premount/sdmem`.
Feature Branch: bugfix/10487-improve-VM-and-OOM-settings-for-erasing-memory
### Related issues
- **Related to** tails/tails#9705
- **Related to** tails/tails#9707
- **Related to** tails/tails#10733
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