Remove -isystem frameworks/av/include

Remove the last -isystem for global include directory (besides
bionic).

Bug: 31751828
Test: builds
Change-Id: I8f38332de8f0cffd5c56b9b5ebeacbaaf3a4faea
Merged-In: I8f38332de8f0cffd5c56b9b5ebeacbaaf3a4faea
(cherry picked from commit d13a457a45d8ebcdf4e248370078c5a5ff88fdcb)
diff --git a/cc/makevars.go b/cc/makevars.go
index ce2ac5a..22b9013 100644
--- a/cc/makevars.go
+++ b/cc/makevars.go
@@ -77,7 +77,7 @@
 
 	ctx.Strict("AIDL_CPP", "${aidlCmd}")
 
-	includeFlags, err := ctx.Eval("${config.CommonGlobalIncludes} ${config.CommonGlobalSystemIncludes}")
+	includeFlags, err := ctx.Eval("${config.CommonGlobalIncludes}")
 	if err != nil {
 		panic(err)
 	}