[ci] Remove ubuntu18.04 job due for the GHA deprecation

Author: kateinoigakukun

.github/scripts/build-matrix.rb

@@ -2,18 +2,19 @@
 require "optparse"
 
 BASE_MATRIX_ENTRIES = [
-  {
-    "build_os": "ubuntu-18.04",
-    "agent_query": "ubuntu-18.04",
-    "target": "ubuntu18.04_x86_64",
-    "container": "ghcr.io/swiftwasm/swift-ci:main-ubuntu-18.04",
-    "run_stdlib_test": true,
-    "run_full_test": false,
-    "run_e2e_test": true,
-    "build_hello_wasm": true,
-    "clean_build_dir": false,
-    "free_disk_space": true
-  },
+# DEPRECATED: GitHub Actions won't support Ubuntu 18.0.4 faimily anymore
+#  {
+#    "build_os": "ubuntu-18.04",
+#    "agent_query": "ubuntu-18.04",
+#    "target": "ubuntu18.04_x86_64",
+#    "container": "ghcr.io/swiftwasm/swift-ci:main-ubuntu-18.04",
+#    "run_stdlib_test": true,
+#    "run_full_test": false,
+#    "run_e2e_test": true,
+#    "build_hello_wasm": true,
+#    "clean_build_dir": false,
+#    "free_disk_space": true
+#  },
   {
     "build_os": "ubuntu-20.04",
     "agent_query": "ubuntu-20.04",

.github/workflows/nightly-distribution.yml

@@ -10,7 +10,7 @@ jobs:
         include:
           - branch: "swiftwasm"
             channel: "DEVELOPMENT"
-            targets: "amazonlinux2_x86_64 ubuntu18.04_x86_64 ubuntu20.04_x86_64 ubuntu20.04_aarch64 ubuntu22.04_x86_64 macos_x86_64 macos_arm64"
+            targets: "amazonlinux2_x86_64 ubuntu20.04_x86_64 ubuntu20.04_aarch64 ubuntu22.04_x86_64 macos_x86_64 macos_arm64"
           - branch: "swiftwasm-release/5.3"
             channel: "5.3"
             targets: "ubuntu18.04_x86_64 ubuntu20.04_x86_64 macos_x86_64"
@@ -28,7 +28,7 @@ jobs:
             targets: "amazonlinux2_x86_64 ubuntu18.04_x86_64 ubuntu20.04_x86_64 ubuntu20.04_aarch64 ubuntu22.04_x86_64 macos_x86_64 macos_arm64"
           - branch: "swiftwasm-release/5.8"
             channel: "5.8"
-            targets: "amazonlinux2_x86_64 ubuntu18.04_x86_64 ubuntu20.04_x86_64 ubuntu20.04_aarch64 ubuntu22.04_x86_64 macos_x86_64 macos_arm64"
+            targets: "amazonlinux2_x86_64 ubuntu20.04_x86_64 ubuntu20.04_aarch64 ubuntu22.04_x86_64 macos_x86_64 macos_arm64"
     steps:
       - uses: actions/checkout@v1
       - name: Setup keychain