tracing: probes: error if BTF is required but unavailable

traceprobe_expand_meta_args expands probe arguments based on BTF info.

Return an error if we have arguments that need expanding but BTF is not
supported.

The params variable is now unused, it can be removed.

Link: https://lore.kernel.org/all/20261014083838.31020-1-martin@kaiser.cx/

Fixes: d157d7694460 ("tracing/probes: Support BTF field access from $retval")
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>