fix: make the Explore Delete buttons send the GP DELETE APDU (v3.6.6)

ramDeleteFromExplorer() called an undefined `_ber_len()` helper, so clicking
Delete / Delete All raised a ReferenceError right after the confirm and no
APDU was ever sent.  The inline builder also omitted the mandatory Le byte.

- new pure `ramDeleteApdu(aid, withCascade)` = GP Card Spec v2.3.1 Table
  11-20/23 form: `80 E4 00 <p2> <Lc> 4F <len> <AID> 00` (P2 00 = object,
  80 = object and related objects), used by the Explore handler.
- `scp81DeleteApdus()` (the "Delete AID" script template) now shares the
  same builder: it used to send the raw AID without the mandatory '4F' TLV.
- tests: exact bytes for 7/16-byte AIDs and both P2 modes, the SCP81 script
  expectations updated to the TLV form, and a wiring check that the undefined
  helper call does not come back (`_ber_len(`).

611 frontend / 495 Python green; version 3.6.6; sw simple-v279.

pysim_simple_server/server.py

@@ -31,7 +31,7 @@ from osmocom.tlv import BER_TLV_IE
 from osmocom.utils import rpad
 
 
-VERSION = '3.6.5'
+VERSION = '3.6.6'
 
 MAX_ENVELOPE_SEGMENTS = 5  # max SMS segments for outgoing C-APDU in ENVELOPE