testsuite: fix invalid option in test

Problem: In a test in t2800-jobs-cmd.t, both the --filter and
--all option are specified, leading to unexpected output.  The
test happens to pass, but may not behave as intended.

Remove the -a option in the test.

t/t2800-jobs-cmd.t

@@ -182,7 +182,7 @@ test_expect_success 'flux-jobs: custom format with numeric spec works' '
 test_expect_success 'flux-jobs: collapsible fields work' '
 	flux jobs -ao "{id.f58:<12} ?:{exception.type:>8}" >nocollapse.out &&
 	flux jobs -f running,completed \
-		-ao "{id.f58:<12} ?:{exception.type:>8}"   >collapsed.out &&
+		 -o "{id.f58:<12} ?:{exception.type:>8}"   >collapsed.out &&
 	test_debug "head -n1 nocollapse.out" &&
 	test_debug "head -n1 collapsed.out" &&
 	grep EXCEPTION-TYPE nocollapse.out &&