init: Remove "select SRCU"

Now that the SRCU Kconfig option is unconditionally selected, there is
no longer any point in selecting it.  Therefore, remove the "select SRCU"
Kconfig statements.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>