Fix command line interface for math_brute_force (#1145)

Ensure the following forms of command lines are supported, as per usage
message (-h):
 - math_brute_force [<name1> [<name2> ... [<nameN>]]]
 - math_brute_force I [J]

Remove dead/unnecessary code.

Fix regression introduced in f337e0b6 ( Fix command-line function range
for bruteforce  (#1127), 2021-01-29).

Signed-off-by: Marco Antognini <marco.antognini@arm.com>

test_conformance/math_brute_force/main.cpp

@@ -140,7 +140,8 @@ int doTest(const char *name)
         const Func *const temp_func = functionList + i;
         if (strcmp(temp_func->name, name) == 0)
         {
-            if (i < gStartTestNumber || i > gEndTestNumber)
+            if ((gStartTestNumber != -1 && i < gStartTestNumber)
+                || i > gEndTestNumber)
             {
                 vlog("Skipping function #%d\n", i);
                 return 0;
@@ -844,10 +845,6 @@ int main(int argc, const char *argv[])
          "----------------------------------------\n");
 
     gMTdata = init_genrand(gRandomSeed);
-    if (gEndTestNumber == 0)
-    {
-        gEndTestNumber = functionListCount;
-    }
 
     FPU_mode_type oldMode;
     DisableFTZ(&oldMode);