env: add ENV_ERASE_PTR macro

Add ENV_ERASE_PTR macro to handle erase opts and remove the associated
ifdef.

This patch is a extension of previous commit 82b2f4135719 ("env_internal.h:
add alternative ENV_SAVE_PTR macro").

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
3 files changed