Cirrus CI: don't install and use MSYS2, don't run a login shell.

Author: guyharris

.cirrus.yml

@@ -75,7 +75,6 @@ windows_task:
     - choco install --no-progress -y winflexbison
     - win_flex --version
     - win_bison --version
-    - choco install -y --no-progress msys2
     - choco install --no-progress -y curl
     - curl -O -s https://www.winpcap.org/install/bin/WpdPack_4_1_2.zip
     - 7z x .\WpdPack_4_1_2.zip -oc:\projects\libpcap\Win32
@@ -84,7 +83,7 @@ windows_task:
     - curl -o AirPcap_Devpack.zip -L -s "https://support.riverbed.com/bin/support/download?sid=l3vk3eu649usgu3rj60uncjqqu"
     - 7z x .\AirPcap_Devpack.zip -oc:\projects\libpcap\Win32
   script:
-   - C:\tools\msys64\usr\bin\bash -lc ".\\build_matrix.sh"
+   - sh -c ".\\build_matrix.sh"
 
 coverity_task:
   name: Coverity Scan