fw_env: remove duplicated definitions

Since commit d3716dd6 ("env: Rename the redundancy flags"), the
definitions of ENV_REDUND_OBSOLETE & ENV_REDUND_ACTIVE was moved
to env.h.

Fixes:

tools/env/fw_env.c:122:22: error: ‘ENV_REDUND_ACTIVE’ redeclared as different kind of symbol
 static unsigned char ENV_REDUND_ACTIVE = 1;
                      ^~~~~~~~~~~~~~~~~
In file included from tools/env/fw_env.c:13:
include/env.h:63:2: note: previous definition of ‘ENV_REDUND_ACTIVE’ was here
  ENV_REDUND_ACTIVE = 1,
  ^~~~~~~~~~~~~~~~~
tools/env/fw_env.c:127:22: error: ‘ENV_REDUND_OBSOLETE’ redeclared as different kind of symbol
 static unsigned char ENV_REDUND_OBSOLETE;
                      ^~~~~~~~~~~~~~~~~~~
In file included from tools/env/fw_env.c:13:
include/env.h:62:2: note: previous definition of ‘ENV_REDUND_OBSOLETE’ was here
  ENV_REDUND_OBSOLETE = 0,

Signed-off-by: Pierre-Jean Texier <pjtexier@koncepto.io>
Tested-by: Joris Offouga <offougajoris@gmail.com>
Tested-by: Heiko Schocher <hs@denx.de>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>