Remove \n from errx and die messages

errx() already appends \n internally. "\n" in the error message will
result in a blank line after the message. die() is just a wrapper around
errx() so it receives the same treatment.

testcases/inject_randr1.5.c

@@ -402,7 +402,7 @@ int main(int argc, char *argv[]) {
     }
 
     if (optind >= argc) {
-        errx(EXIT_FAILURE, "syntax: %s [options] <command>\n", argv[0]);
+        errx(EXIT_FAILURE, "syntax: %s [options] <command>", argv[0]);
     }
 
     int fd = socket(AF_LOCAL, SOCK_STREAM, 0);