Shell/alias: Print detailed error when deleting alias

STR_GEN_ERR_NOT_FOUND is added and currently is only
used by alias command. This string template can be used
by other commands as well.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Tapan Shah <tapandshah@hpe.com>
(cherry picked from commit 937bc66e1e555e74acdeba766b12c06fd506e408)
2 files changed