[Infra] Removed CapNProto Subtree Folder

In order to upgrade CapNProto to a new version (simply), had to remove
the old folder entirely before upgrading to a new version.

Due to how the subtree script works, this must be done in its own
commit.

Author: AlexandreSinger

dev/subtree_config.xml

@@ -33,7 +33,7 @@
         name="capnproto"
         internal_path="libs/EXTERNAL/capnproto"
         external_url="https://github.com/capnproto/capnproto.git"
-        default_external_ref="v0.9.1"/>
+        default_external_ref="v1.0.2"/>
     <subtree
         name="libinterchange"
         internal_path="libs/EXTERNAL/libinterchange"