env: mcc: Drop unnecessary #ifdefs

This file has a lot of conditional code and much of it is unnecessary.
Clean this up to reduce the number of build combinations.

This patch replaces the test on CONFIG_ENV_OFFSET_REDUND for the
more coherent CONFIG_SYS_REDUNDAND_ENVIRONMENT.

This patch also corrects a compilation issue in init_mmc_for_env()
when CONFIG_SYS_MMC_ENV_PART is not activated, env_mmc_orig_hwpart is
not defined.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>