Auto merge of #19181 - mbrubeck:opts, r=emilio

Remove unused -t command-line flag

A little bit was left over from #16716.

- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because they only remove unused code

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components/config/opts.rs

@@ -569,7 +569,6 @@ pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
     opts.optopt("o", "output", "Output file", "output.png");
     opts.optopt("s", "size", "Size of tiles", "512");
     opts.optopt("", "device-pixel-ratio", "Device pixels per px", "");
-    opts.optopt("t", "threads", "Number of paint threads", "1");
     opts.optflagopt("p", "profile", "Time profiler flag and either a TSV output filename \
         OR an interval for output to Stdout (blank for Stdout with interval of 5s)", "10 \
         OR time.tsv");