conversions: remove timing functionality (#2394)

Remove the test timing functionality from the conversions test, because
it

 - is not advertised in the help,

- is not supported on all platforms, triggering warnings during the
build,

 - goes beyond the core purpose of the conformance test suite.

Signed-off-by: Sven van Haastregt <sven.vanhaastregt@arm.com>

test_conformance/conversions/test_conversions.cpp

@@ -226,8 +226,6 @@ static int ParseArgs(int argc, const char **argv)
                         gForceFTZ ^= 1;
                         gForceHalfFTZ ^= 1;
                         break;
-                    case 't': gTimeResults ^= 1; break;
-                    case 'a': gReportAverageTimes ^= 1; break;
                     case '1':
                         if (arg[1] == '6')
                         {