tools: moveconfig: fix cleanup of defines across multiple lines
Correct the clean-up of such defines that continue across multiple
lines, like follows:
#define CONFIG_FOO "this continues to the next line " \
"this line should be removed too" \
"this line should be removed as well"
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Tom Rini <trini@konsulko.com>