camdd: Remove some dead code but also make -E functional.

• Pass down the top-level arglist from main down to camdd_rw and use it in place of the hardcoded CAMDD_ARG_ERR_RECOVER when calling camdd_probe_pass. This now disables error recovery by default unless -E is specified.

• Use the return value of parse_btl to determine if an explicit LUN was specified.

• Remove most CAMDD_ARG_* flags that are only set and never checked. CAMDD_ARG_VERBOSE remains, but could perhaps be removed (and possibly -v should be removed as well since it is currently a no-op).

Reported by: clang -Wunused-but-set-variable (arglist in main)
Differential Revision: https://reviews.freebsd.org/D40666