genksyms: generate lexer and parser during build instead of shipping

Now that the kernel build supports flex and bison, remove the _shipped
files and generate them during the build instead.

There are no more shipped lexer and parser, so I ripped off the rules
in scripts/Malefile.lib that were used for REGENERATE_PARSERS.

The genksyms parser has ambiguous grammar, which would emit warnings:

 scripts/genksyms/parse.y: warning: 9 shift/reduce conflicts [-Wconflicts-sr]
 scripts/genksyms/parse.y: warning: 5 reduce/reduce conflicts [-Wconflicts-rr]

They are normally suppressed, but displayed when W=1 is given.

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