kconfig: stop adding P_SYMBOL property to symbols

I believe its last usage was in the following code:

if (prop == NULL)
prop = stack->sym->prop;

This code was previously used to print the file name and line number of
associated symbols in sym_check_print_recursive(), which was removed by
commit 9d0d26604657 ("kconfig: recursive checks drop file/lineno").

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>