csky: remove deprecated arch/csky/boot/dts/include/dt-bindings

Having a symbolic link arch/*/boot/dts/include/dt-bindings was
deprecated by commit d5d332d3f7e8 ("devicetree: Move include
prefixes from arch to separate directory").

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

diff --git a/arch/csky/boot/dts/include/dt-bindings b/arch/csky/boot/dts/include/dt-bindings
deleted file mode 120000 (symlink)
index 08c00e4..0000000
--- a/arch/csky/boot/dts/include/dt-bindings
+++ /dev/null
@@ -1 +0,0 @@
-../../../../../include/dt-bindings
\ No newline at end of file