Remove arm64 build

Arm64 builds are not built for 1.7.x

.circleci/config.yml

@@ -10,15 +10,6 @@ jobs:
       - checkout
       - run: script/cibuild
 
-  electron-linux-arm64:
-    docker:
-      - image: electronbuilds/electron:0.0.3
-        environment:
-          TARGET_ARCH: arm64
-    steps:
-      - checkout
-      - run: script/cibuild
-
   electron-linux-ia32:
     docker:
       - image: electronbuilds/electron:0.0.3
@@ -42,9 +33,6 @@ workflows:
   build-arm:
     jobs:
       - electron-linux-arm
-  build-arm64:
-    jobs:
-      - electron-linux-arm64
   build-ia32:
     jobs:
       - electron-linux-ia32