kernel: disable CONFIG_RCU_EXPERT and friends

kernel: disable CONFIG_RCU_EXPERT and friends

Based on the existing documentation [1][2], I dare anyone to demonstrate that
we need to fine-tune these RCU parameters. The (performance) breakage potential
for doing so is immense, so let's just please put down this loaded footgun.

Disable CONFIG_RCU_EXPERT and its dependent symbols. Additionally, remove the
CONFIG_RCU_EXPERT symbol from the target kconfigs which contain it.

[1] https://www.kernel.org/doc/Documentation/RCU/Design/Data-Structures/Data-Structures.html
[2] https://lwn.net/Articles/777214/

Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>