Strip PCIe-M2 (M-key/NVMe) sheet; re-baseline stripped carrier

Drops the unused M.2 M-key/NVMe block — design is 1x M.2 E-key (Wi-Fi)
only, since the CM5 exposes a single PCIe x1 lane (datasheet SC1466),
reserved for the E-key. The 10 freed PCIE_* lanes are NC on Module1
unit 2, to be rewired to a fresh E-key sheet in the add phase.

- CM5_HighSpeed: retire PCIE_* labels/wires, NC pins 102,104,106,109,
  110,112,116,118,122,124
- root CM5IO: drop whole PCIe-M2 (sheet) block; strip dangling PCIE_*
  pins off the kept CM5_HighSpeed sheet symbol
- delete carrier/PCIe-M2.kicad_sch; clean .kicad_pro sheets array + ERC
  exclusion
- retire_block.py: add --drop-sheet FILE (remove whole (sheet) block +
  sheet_instances path)
- analysis/baseline/carrier_stripped.json: new add-phase diff anchor

Verify: ERC 136->133 (zero new violation types); analyzer diff +0/~0
(cumulative -41 removed vs original ref); netlist confirms +5v/+3.3v/
GND/+1.8v intact (U8's M2_3v3 was a local rail, not board +3.3v).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

carrier/CM5IO.kicad_pro

@@ -261,7 +261,6 @@
   "erc": {
     "erc_exclusions": [
       "power_pin_not_driven|1003300|1181100|66cf9899-100d-45fb-9b9f-8f866de8a3fe|00000000-0000-0000-0000-000000000000|/e63e39d7-6ac0-4ffd-8aa3-1841a4541b55/00000000-0000-0000-0000-00005cff706a|/e63e39d7-6ac0-4ffd-8aa3-1841a4541b55/00000000-0000-0000-0000-00005cff706a|",
-      "power_pin_not_driven|1524000|317500|2cecda96-8fc5-40d2-a9f4-ae1444adbd06|00000000-0000-0000-0000-000000000000|/e63e39d7-6ac0-4ffd-8aa3-1841a4541b55/00000000-0000-0000-0000-00005ed4bb5b|/e63e39d7-6ac0-4ffd-8aa3-1841a4541b55/00000000-0000-0000-0000-00005ed4bb5b|",
       "power_pin_not_driven|393700|1181100|0fc4267c-2119-444e-b3b2-d8a7bd88ec8a|00000000-0000-0000-0000-000000000000|/e63e39d7-6ac0-4ffd-8aa3-1841a4541b55/00000000-0000-0000-0000-00005cff706a|/e63e39d7-6ac0-4ffd-8aa3-1841a4541b55/00000000-0000-0000-0000-00005cff706a|"
     ],
     "meta": {
@@ -834,10 +833,6 @@
     [
       "00000000-0000-0000-0000-00005cff706a",
       "CM5_GPIO ( Ethernet, GPIO, SDCARD)"
-    ],
-    [
-      "00000000-0000-0000-0000-00005ed4bb5b",
-      "PCIe-M2"
     ]
   ],
   "text_variables": {}