Delete Gitlab CI config

We're not using Gitlab's CI anyway, and they don't offer free Mac
build bots at this time, either. It just keeps spamming me with build
failure notices every time I push commits to that mirror.

Signed-off-by: Christopher Snowhill <kode54@gmail.com>

.gitlab-ci.yml

@@ -1,23 +0,0 @@
-.macos_saas_runners:
-  tags:
-    - shared-macos-amd64
-  image: macos-11-xcode-13
-
-variables:
-  GIT_SUBMODULE_STRATEGY: recursive
-
-stages:
-  - build
-
-build_project:
-  extends:
-    - .macos_saas_runners
-  stage: build
-  script:
-    - cp "$DEV_TEAM_FILE" Xcode-config/DEVELOPMENT_TEAM.xcconfig
-    - xcodebuild -workspace "./Cog.xcodeproj/project.xcworkspace" -scheme Cog -configuration Release -derivedDataPath "./CogBuilds" CODE_SIGNING_ALLOWED=NO ONLY_ACTIVE_ARCH=NO build
-    - ditto -c -k --sequesterRsrc --keepParent  "./CogBuilds/Build/Products/Release/Cog.app" "./CogBuilds/Cog.app.zip" 
-  artifacts:
-    paths: 
-    - ./CogBuilds/Cog.app.zip
-    expire_in: 1 week