remove ubuntu 18 from CI test OS matrix (#187)

* remove ubuntu 18 from CI build and run OS matrix

* Remove ubuntu18 specific instruction from CI

.github/workflows/pr-test.yml

@@ -7,7 +7,7 @@ jobs:
 
     strategy:
       matrix:
-        os: [ubuntu-18.04, ubuntu-latest, windows-2019, windows-latest]
+        os: [ubuntu-latest, windows-2019, windows-latest]
 
     # Use bash for Windows as well.
     defaults:
@@ -22,13 +22,7 @@ jobs:
     - name: Install dependencies
       if: runner.os != 'Windows'
       run: |
-        if [ "${{ matrix.os }}" != "ubuntu-18.04" ]; then
-            sudo apt install cmake g++ libaio-dev libgoogle-perftools-dev libunwind-dev clang-format libboost-dev libboost-program-options-dev libmkl-full-dev
-        else
-            sudo apt install cmake g++ libaio-dev libgoogle-perftools-dev clang-format libboost-dev libboost-program-options-dev
-            wget https://registrationcenter-download.intel.com/akdlm/irc_nas/18487/l_BaseKit_p_2022.1.2.146.sh
-            sudo sh l_BaseKit_p_2022.1.2.146.sh -a --components intel.oneapi.lin.mkl.devel --action install --eula accept -s
-        fi
+        sudo apt install cmake g++ libaio-dev libgoogle-perftools-dev libunwind-dev clang-format libboost-dev libboost-program-options-dev libmkl-full-dev
     - name: Ubuntu CMake Configure
       if: runner.os != 'Windows'
       run: |