dumpstate: remove -std=gnu99

-std=gnu99 no longer has effect now that dumpstate is C++.

The flag also break build if target platform is configured to default
gcc compiler since gcc throws warning for having -std=gnu99 when compiling
C++ and we have -Werror for the module.

Reproduce:
mm LOCAL_CLANG=false
...
error: command line option '-std=gnu99' is valid for C/ObjC but not for C++ [-Werror]

Change-Id: If1c272868ec4626873e7d91342b1fea51a15c52e
diff --git a/cmds/dumpstate/Android.mk b/cmds/dumpstate/Android.mk
index a4b5ff1..a588ef4 100644
--- a/cmds/dumpstate/Android.mk
+++ b/cmds/dumpstate/Android.mk
@@ -18,7 +18,7 @@
 # ZipArchive support, the order matters here to get all symbols.
 LOCAL_STATIC_LIBRARIES := libziparchive libz libbase libmincrypt
 LOCAL_HAL_STATIC_LIBRARIES := libdumpstate
-LOCAL_CFLAGS += -Wall -Werror -Wno-unused-parameter -std=gnu99
+LOCAL_CFLAGS += -Wall -Werror -Wno-unused-parameter
 LOCAL_INIT_RC := dumpstate.rc
 
 include $(BUILD_EXECUTABLE)