Delete DexpreoptGlobalConfig entry after deleting the file it points to

Make creates out/soong/dexpreopt.config, but art/tools/build_linux_bionic.sh
deletes the file.  Delete the config entry too so that Soong doesn't
fail to open it.

Test: art/tools/build_linux_bionic.sh
Change-Id: I63f203a4d73b926d1affdab70c73c3f061cfe03d
diff --git a/tools/build_linux_bionic.sh b/tools/build_linux_bionic.sh
index b401071..0a933d4 100755
--- a/tools/build_linux_bionic.sh
+++ b/tools/build_linux_bionic.sh
@@ -81,6 +81,8 @@
 x['CrossHostArch'] = 'x86_64'
 if 'CrossHostSecondaryArch' in x:
   del x['CrossHostSecondaryArch']
+if 'DexpreoptGlobalConfig' in x:
+  del x['DexpreoptGlobalConfig']
 json.dump(x, open(sys.argv[2], mode='w'))
 END