tools: bpftool: remove spurious line break from error message

The end-of-line character inside the string would break JSON compliance.
Remove it, `p_err()` already adds a '\n' character for plain output
anyway.

Fixes: 9a5ab8bf1d6d ("tools: bpftool: turn err() and info() macros into functions")
Reported-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/bpf/bpftool/main.h

@@ -51,7 +51,7 @@
 
 #define NEXT_ARG()	({ argc--; argv++; if (argc < 0) usage(); })
 #define NEXT_ARGP()	({ (*argc)--; (*argv)++; if (*argc < 0) usage(); })
-#define BAD_ARG()	({ p_err("what is '%s'?\n", *argv); -1; })
+#define BAD_ARG()	({ p_err("what is '%s'?", *argv); -1; })
 
 #define ERR_MAX_LEN	1024