axolotl: Remove IO read_ahead_kb tune

If we set 2048KB ra value in the beginning of the
boot process, services initialized at this time would
keep 2048KB ra value even though we adjust the ra value
to 128KB after boot completion.

This may cause memory pressure.

Bug: 174700194
Signed-off-by: Randall Huang <huangrandall@google.com>
Change-Id: I97ee0ee9511eaada011f2634afd68d68cdca4570