Remove external/c-ares from manifest.

Nothing in Android references this anymore.

default.xml

@@ -104,7 +104,6 @@
   <project path="external/brotli" name="platform/external/brotli" groups="pdk" />
   <project path="external/bsdiff" name="platform/external/bsdiff" groups="pdk" />
   <project path="external/bzip2" name="platform/external/bzip2" groups="pdk" />
-  <project path="external/c-ares" name="platform/external/c-ares" groups="pdk" />
   <project path="external/caliper" name="platform/external/caliper" groups="pdk" />
   <project path="external/cblas" name="platform/external/cblas" groups="pdk" />
   <project path="external/chromium-libpac" name="platform/external/chromium-libpac" groups="pdk" />