fs: VALIDATE_FS_PARSER should default to n

CONFIG_VALIDATE_FS_PARSER is a debugging tool to check that the parser
tables are vaguely sane.  It was set to default to 'Y' for the moment to
catch errors in upcoming fs conversion development.

Make sure it is not enabled by default in the final release of v5.1.

Fixes: 31d921c7

 ("vfs: Add configuration parser helpers")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>