Remove unnecessary ret value control when spec test is enabled (#1839)

wamr-test-suites scripts can handle the return value correctly when
spec test is enabled.

Author: wenyongh

product-mini/platforms/linux-sgx/enclave-sample/App/App.cpp

@@ -796,12 +796,7 @@ main(int argc, char *argv[])
     /* Destroy runtime environment */
     destroy_runtime();
 
-#if WASM_ENABLE_SPEC_TEST != 0
-    (void)ret;
-    return 0;
-#else
     return ret;
-#endif
 }
 
 int

product-mini/platforms/posix/main.c

@@ -696,10 +696,5 @@ main(int argc, char *argv[])
     /* destroy runtime environment */
     wasm_runtime_destroy();
 
-#if WASM_ENABLE_SPEC_TEST != 0
-    (void)ret;
-    return 0;
-#else
     return ret;
-#endif
 }

product-mini/platforms/windows/main.c

@@ -496,10 +496,5 @@ main(int argc, char *argv[])
     /* destroy runtime environment */
     wasm_runtime_destroy();
 
-#if WASM_ENABLE_SPEC_TEST != 0
-    (void)ret;
-    return 0;
-#else
     return ret;
-#endif
 }