Use -Werror in hardware/libhardware/tests

* Remove unused local variables.
* Suppress warning of unused template functions.
* Fix error of unused expression value.

Bug: 66996870
Test: build with WITH_TIDY=1
Change-Id: I5a37c24f3be0f61b0ae4552e34b7311f561d499e
diff --git a/tests/hwc/cnativewindow.c b/tests/hwc/cnativewindow.c
index 5b1d78e..65a814d 100644
--- a/tests/hwc/cnativewindow.c
+++ b/tests/hwc/cnativewindow.c
@@ -181,7 +181,7 @@
 	hwc_composer_device_1_t *hwc = win->hwc;
 	hwc_display_contents_1_t *dc = &(win->dc);
 	hwc_layer_1_t *dl = win->dc.hwLayers;
-	int r, i;
+	int r;
 
 	dc->retireFenceFd = -1;
 	dc->outbufAcquireFenceFd = -1;
@@ -462,8 +462,8 @@
 	hw_module_t const* module;
 	framebuffer_device_t *fb = NULL;
 	alloc_device_t *gr;
-	int err, i, n;
-	unsigned usage, format;
+	int err, i;
+	unsigned usage;
 
 	memset(win, 0, sizeof(CNativeWindow));