Refactor: based, libcib: Drop cib_operation_t:prepare

The logic is simple enough to condense into a single prepare function in
based_callbacks.c. The existing prepare functions all returned pcmk_ok
unconditionally.

cib_prepare_none() is basically a special case of cib_prepare_data() --
F_CIB_CALLDATA should not be set for requests that used
cib_prepare_none(), and the processor functions shouldn't try to use it.

cib_prepare_sync() is identical to cib_prepare_none().

cib_prepare_diff() is used only for PCMKCIB_REQUEST_APPLY_PATCH, so we
can check for cibop_apply_patch directly.

Also drop extern declaration of cib_perform_command(), which does not
exist.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>