Drop fabricated SET UP IDLE MODE TEXT qualifier decode; bump to 1.15.1

Spec verification against UICC_SPECS.md / TS 102 223 V18.3.0 §8.6
showed the Command Qualifier for SET UP IDLE MODE TEXT is RFU
("this byte is RFU") — no icon self-explanatory bit exists in any
generation (GSM 11.14 predates the command; TS 31.111 does not
override it). The v1.11.0 _idle_text_qualifier decoded bit 1 as
"icon self-explanatory" from an unverified source.

Remove the decoder; the command now uses generic RFU handling
(hidden at '00', raw hex otherwise). Tests updated accordingly.
Version 1.15.1, SW cache v21.

simtrace2_pysniff/server/decode.py

@@ -1069,20 +1069,9 @@ COMMAND_QUALIFIERS = {
     0x01: REFRESH_MODES,   # REFRESH
     0x26: PLI_QUALIFIERS,  # PROVIDE LOCAL INFORMATION
 }
-
-
-def _idle_text_qualifier(qualifier):
-    """SET UP IDLE MODE TEXT (TS 102 223 §6.6.13): bit 1 = icon
-    self-explanatory flag, all other bits RFU."""
-    if qualifier & ~0x01:
-        return f'0x{qualifier:02X}'
-    if qualifier & 0x01:
-        return 'icon self-explanatory'
-    return None
-
-
-# TS 102 223 §6.6.13 — SET UP IDLE MODE TEXT
-COMMAND_QUALIFIERS[0x28] = _idle_text_qualifier
+# NOTE: SET UP IDLE MODE TEXT ('28') has no entry — its Command Qualifier
+# is RFU per TS 102 223 V18.3.0 §8.6 ("this byte is RFU"); the generic
+# fallback (hidden at '00', raw hex otherwise) applies.
 
 
 # ──────────────────── §8.6 bitmask qualifier decoders ────────────────────