ctf: rename ctx_create to ctf_visitor_generate_ir_create

ctf: rename ctx_create to ctf_visitor_generate_ir_create

There is an unnecessary level here, rename the existing ctx_create to
ctf_visitor_generate_ir_create.  Remove the existing
ctf_visitor_generate_ir_create.

Change-Id: I2ce578f30e1e9e25754dc9ad4f18610eb3a0be36
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8424
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12743