kconfig: remove P_ENV property type

This property is not set by anyone since commit 104daea149c4 ("kconfig:
reference environment variables directly and remove 'option env='").

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
3 files changed