Don't specify the common CFLAGS

These are already defined by the global GN configuration for all
Fuchsia projects and shouldn't be set on per-project basis unless
necessary, in which case they need to carefully set to avoid
collisions with the default flags.

Change-Id: Id1f1a1ac627338824c3b14c23ee8fee030e6c8fa
diff --git a/wpa_supplicant/BUILD.gn b/wpa_supplicant/BUILD.gn
index 9452cb5..8eefab5 100644
--- a/wpa_supplicant/BUILD.gn
+++ b/wpa_supplicant/BUILD.gn
@@ -26,11 +26,6 @@
   ]
 
   cflags = [
-    "-MMD",
-    "-O2",
-    "-g",
-    "-Wall",
-    "-Wextra",
     "-Wno-unused-function",
     "-Wno-unused-parameter",
   ]