env: common: Drop env_get_char_memory()

env: common: Drop env_get_char_memory()

This function is the same as env_get_char_spec() apart from dropping the
brackets. Drop the brackets from env_get_char_spec() and use that instead
of env_get_char_memory().

Signed-off-by: Simon Glass <[email protected]>
Reviewed-by: Tom Rini <[email protected]>