Clean up podspec: drop redundant libxml2 flag and requires_arc

- Remove `-I$(SDKROOT)/usr/include/libxml2` from the WebDAV subspec: the
  modern SDK ships a libxml2 module map that resolves <libxml/parser.h>
  with no extra header search path (verified via pod lib lint).
- Remove all `requires_arc = true` declarations: ARC is the CocoaPods
  default and the sources already enforce it with #error guards. They
  were leftovers from when GCDWebServer <= 3.1 supported MRC.
- Remove the leftover pod trunk template comment block.

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

.vscode/launch.json

@@ -0,0 +1,24 @@
+{
+    "configurations": [
+        {
+            "type": "swift",
+            "request": "launch",
+            "args": [],
+            "cwd": "${workspaceFolder:GCDWebServer}",
+            "name": "Debug _spmcheck",
+            "target": "_spmcheck",
+            "configuration": "debug",
+            "preLaunchTask": "swift: Build Debug _spmcheck"
+        },
+        {
+            "type": "swift",
+            "request": "launch",
+            "args": [],
+            "cwd": "${workspaceFolder:GCDWebServer}",
+            "name": "Release _spmcheck",
+            "target": "_spmcheck",
+            "configuration": "release",
+            "preLaunchTask": "swift: Build Release _spmcheck"
+        }
+    ]
+}