vm-monitor: Don't set cgroup memory.max

[sharnoff]

All it does is make postgres OOM more often (which, tbf, means we're less likely to have e.g. compute_ctl get OOM-killed, but that tradeoff isn't worth it).

Internally, this means removing all references to memory.max and the places where we calculate or store the intended value.

As discussed in the sync earlier.

ref:

• https://neondb.slack.com/archives/C03H1K0PGKH/p1694698949252439?thread_ts=1694505575.693449&cid=C03H1K0PGKH
• https://neondb.slack.com/archives/C03H1K0PGKH/p1695049198622759

[github-actions]

2484 tests run: 2367 passed, 0 failed, 117 skipped (full report)

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Flaky tests (7)

Postgres 16

• test_partial_evict_tenant: release, debug
• test_pageserver_recovery: release
• test_get_tenant_size_with_multiple_branches: debug
• test_wal_lagging: release

Postgres 15

• test_crafted_wal_end[last_wal_record_crossing_segment]: debug

Postgres 14

• test_get_tenant_size_with_multiple_branches: release

Code coverage (full report)

• functions: 53.0% (7749 of 14614 functions)
• lines: 81.0% (45231 of 55824 lines)

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_{The comment gets automatically updated with the latest test results
fad94f6 at 2023-09-18T18:31:23.001Z :recycle:}