fix(kernel): remove slub_debug kernel param

[andrewrynhard]

With slub_debug=P the following occurred when spinning up an EC2 instance with an AMI built from the Dianemo docker container:

2018/10/14 15:07:33.111170 main.go:44: initializing mount points
[   31.798655] XFS (xvda2): Mounting V5 Filesystem
[   31.831006] XFS (xvda2): Metadata CRC error detected at xfs_agi_read_verify+0xc6/0xf0, xfs_agi block 0x2 
[   31.839450] XFS (xvda2): Unmount and run xfs_repair
[   31.844043] XFS (xvda2): First 128 bytes of corrupted metadata buffer:
[   31.849937] 00000000fe7a10f8: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
[   31.857665] 00000000763e02ae: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
[   31.864996] 00000000885bf2eb: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
[   31.872928] 000000008abf1fb1: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
[   31.881218] 00000000829bd485: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
[   31.889018] 00000000238a97a2: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
[   31.897222] 000000006582036b: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
[   31.905296] 0000000076fa4f16: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff  ................
[   31.913197] XFS (xvda2): metadata I/O error in "xfs_trans_read_buf_map" at daddr 0x2 len 1 error 74
[   31.921894] XFS (xvda2): xfs_imap_lookup: xfs_ialloc_read_agi() returned error -117, agno 0
[   31.929543] XFS (xvda2): Failed to read root inode 0x60, error 117
2018/10/14 15:07:33.261386 main.go:28: recovered from: mount /root: structure needs cleaning
[   31.941627] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000000
[   31.941627] 
[   31.950250] CPU: 0 PID: 1479 Comm: init Tainted: G                T 4.18.13-dianemo #1
[   31.957325] Hardware name: Xen HVM domU, BIOS 4.2.amazon 08/24/2006
[   31.962916] Call Trace:
[   31.965740]  dump_stack+0x5c/0x7b
[   31.969228]  panic+0xdf/0x224
[   31.972427]  do_exit+0xb39/0xb40
[   31.975847]  ? __switch_to_asm+0x40/0x70
[   31.979797]  ? __switch_to_asm+0x34/0x70
[   31.983616]  ? __switch_to_asm+0x40/0x70
[   31.987463]  do_group_exit+0x34/0xb0
[   31.991068]  get_signal+0x280/0x5d0
[   31.994643]  do_signal+0x31/0x570
[   31.998515]  ? do_nanosleep+0xb7/0x190
[   32.006570]  exit_to_usermode_loop+0x5f/0xb0
[   32.015649]  do_syscall_64+0x233/0x301
[   32.019827]  ? __switch_to_asm+0x34/0x70
[   32.023645]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   32.028108] RIP: 0033:0x844a8d
[   32.031153] Code: Bad RIP value.
[   32.034416] RSP: 002b:00007f1cd1ffed80 EFLAGS: 00000202 ORIG_RAX: 0000000000000023
[   32.040990] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000844a8d
[   32.047085] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007f1cd1ffed80
[   32.052881] RBP: 00007f1cd1ffed90 R08: 0000000000000000 R09: 0000000000000000
[   32.058460] R10: 001be51d00000000 R11: 0000000000000202 R12: 00007ffe40eff81e
[   32.063900] R13: 00007ffe40eff81f R14: 00007f1cd1fff700 R15: 0000000000000000
[   32.069291] Kernel Offset: 0x15400000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)

This PR removes the parameter for now until we can figure out the root cause. To reproduce the issue, use the autonomy/dianemo:5ccc909 image to build an AMI.