Revert "Use remote part's implementation of ccache"

This reverts commit 4383a92.

Reason for reversal:
brlin-tw/ccache-part#2

snap/snapcraft.yaml

@@ -361,6 +361,40 @@ parts:
   ccache:
     after:
       - gcc-6
+    override-pull: 'true'
+    build-packages:
+      - ccache
+    plugin: nil
+    override-build: |
+      mkdir \
+        --parents \
+        "${SNAPCRAFT_PART_INSTALL}"/bin
+      ln \
+        --force \
+        --symbolic \
+        "$(which ccache)" \
+        "${SNAPCRAFT_PART_INSTALL}"/bin/gcc-6
+      ln \
+        --force \
+        --symbolic \
+        "$(which ccache)" \
+        "${SNAPCRAFT_PART_INSTALL}"/bin/g++-6
+      ln \
+        --force \
+        --symbolic \
+        ./gcc-6 \
+        "${SNAPCRAFT_PART_INSTALL}"/bin/gcc
+      ln \
+        --force \
+        --symbolic \
+        ./g++-6 \
+        "${SNAPCRAFT_PART_INSTALL}"/bin/g++
+    filesets:
+      executables:
+        - bin/*
+    stage:
+      - $executables
+    override-prime: 'true'
 
   # This pseudo part setups version 6 of GCC, which is not available
   # in Ubuntu 16.04 software source.