drm_hwcomposer: Drop -Wno-unused-* build options and remove unused variables

This patch drops the -Wno-unused-* build options and removes
the currently unused variables that would keep things from
building.

Signed-off-by: John Stultz <john.stultz@linaro.org>
diff --git a/Android.mk b/Android.mk
index 3d48ba5..c212127 100644
--- a/Android.mk
+++ b/Android.mk
@@ -19,11 +19,6 @@
 common_drm_hwcomposer_cflags := \
     -Wall \
     -Werror \
-    -Wno-unused-function \
-    -Wno-unused-label \
-    -Wno-unused-parameter \
-    -Wno-unused-private-field \
-    -Wno-unused-variable \
 
 # =====================
 # libdrmhwc_utils.a
diff --git a/drmdisplaycomposition.cpp b/drmdisplaycomposition.cpp
index 129bec2..aaf78cc 100644
--- a/drmdisplaycomposition.cpp
+++ b/drmdisplaycomposition.cpp
@@ -107,7 +107,6 @@
     to_composite.emplace(std::make_pair(i, &layers_[i]));
 
   int ret;
-  std::vector<DrmCompositionPlane> plan;
   std::tie(ret, composition_planes_) = planner_->ProvisionPlanes(
       to_composite, crtc_, primary_planes, overlay_planes);
   if (ret) {
diff --git a/drmhwctwo.cpp b/drmhwctwo.cpp
index 3ee9f8e..3d0217c 100644
--- a/drmhwctwo.cpp
+++ b/drmhwctwo.cpp
@@ -693,7 +693,6 @@
 HWC2::Error DrmHwcTwo::HwcDisplay::ValidateDisplay(uint32_t *num_types,
                                                    uint32_t *num_requests) {
   supported(__func__);
-  size_t plane_count = 0;
   *num_types = 0;
   *num_requests = 0;
   size_t avail_planes = primary_planes_.size() + overlay_planes_.size();