Removing old ubuntu

.github/workflows/ubuntu18.yml

diff --git a/.github/workflows/ubuntu18.yml b/.github/workflows/ubuntu18.yml
deleted file mode 100644
index 791582d..0000000
--- a/.github/workflows/ubuntu18.yml
+++ /dev/null
@@ -1,26 +0,0 @@
-name: Ubuntu 18.04 CI (GCC 7)
-
-on: [push, pull_request]
-
-jobs:
-  ubuntu-build:
-    runs-on: ubuntu-18.04
-    steps:
-      - uses: actions/checkout@v3
-      - name: Setup cmake
-        uses: jwlawson/actions-setup-cmake@v1.4
-        with:
-          cmake-version: '3.11.x'
-      #- name: Install older compilers
-      #  run: |
-      #    sudo -E dpkg --add-architecture i386
-      #    sudo -E apt-get update
-      #    sudo -E apt-get install -y --force-yes g++-5 g++-6 g++-5-multilib g++-6-multilib g++-multilib linux-libc-dev:i386 libc6:i386 libc6-dev:i386 libc6-dbg:i386
-      - name: Prepare build dir
-        run: mkdir build
-      - name: Configure
-        run: cd build && cmake ${{matrix.cxx}} ${{matrix.arch}} -DFASTFLOAT_TEST=ON ..
-      - name: Build
-        run: cmake --build build
-      - name: Run basic tests
-        run: cd build && ctest --output-on-failure -R basictest