hush: complete renaming CONFIG_SYS_HUSH_PARSER to CONFIG_HUSH_PARSER

There is no more define of CONFIG_SYS_HUSH_PARSER.  Rename some
remaining references and drop the backward compatible Kconfig entry.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/common/Makefile b/common/Makefile
index 34cb898..e08cd3e 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -11,10 +11,7 @@
 obj-y += main.o
 obj-y += exports.o
 obj-y += hash.o
-ifdef CONFIG_SYS_HUSH_PARSER
-obj-y += cli_hush.o
-endif
-
+obj-$(CONFIG_HUSH_PARSER) += cli_hush.o
 obj-$(CONFIG_AUTOBOOT) += autoboot.o
 
 # This option is not just y/n - it can have a numeric value