build: tidy up cares.gyp

Add comment noting that `cares_sources_common` is generated by tooling.
Remove duplicated entries.

PR-URL: #55445
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>

deps/cares/cares.gyp

@@ -1,5 +1,6 @@
 {
   'variables': {
+    # This list is generated by `tools/dep_updaters/update-c-ares.mjs`.
     'cares_sources_common': [
       'include/ares.h',
       'include/ares_build.h',
@@ -135,13 +136,6 @@
     ],
     'cares_sources_mac': [
       'config/darwin/ares_config.h',
-      'src/lib/ares_sysconfig_mac.c',
-      'src/lib/thirdparty/apple/dnsinfo.h',
-    ],
-    'cares_sources_win': [
-      'src/lib/ares_sysconfig_win.c',
-      'src/lib/config-win32.h',
-      'src/lib/windows_port.c',
     ],
   },
 
@@ -203,9 +197,6 @@
             '_WINSOCK_DEPRECATED_NO_WARNINGS',
           ],
           'include_dirs': [ 'config/win32' ],
-          'sources': [
-            '<@(cares_sources_win)',
-          ],
           'libraries': [
             '-lws2_32.lib',
             '-liphlpapi.lib'