ci: revert msys2 ca-certificates hack

The hack was added because upstream msys2 broke the ca-certificates
package, but since then it has been fixed. This reverts CI to use the
upstream package.

Author: pietroalbini

src/ci/azure-pipelines/steps/install-windows-build-deps.yml

@@ -84,17 +84,6 @@ steps:
   condition: and(succeeded(), eq(variables['Agent.OS'], 'Windows_NT'), ne(variables['MINGW_URL'],''))
   displayName: Download custom MinGW
 
-# FIXME(#65767): workaround msys bug, step 1
-- bash: |
-    set -e
-    arch=i686
-    if [ "$MSYS_BITS" = "64" ]; then
-      arch=x86_64
-    fi
-    curl -O https://ci-mirrors.rust-lang.org/rustc/msys2-repo/mingw/$arch/mingw-w64-$arch-ca-certificates-20180409-1-any.pkg.tar.xz
-  condition: and(succeeded(), eq(variables['Agent.OS'], 'Windows_NT'))
-  displayName: Download working ca-certificates for msys
-
 # Otherwise install MinGW through `pacman`
 - bash: |
     set -e
@@ -107,18 +96,6 @@ steps:
   condition: and(succeeded(), eq(variables['Agent.OS'], 'Windows_NT'), eq(variables['MINGW_URL'],''))
   displayName: Download standard MinGW
 
-# FIXME(#65767): workaround msys bug, step 2
-- bash: |
-    set -e
-    arch=i686
-    if [ "$MSYS_BITS" = "64" ]; then
-      arch=x86_64
-    fi
-    pacman -U --noconfirm --noprogressbar mingw-w64-$arch-ca-certificates-20180409-1-any.pkg.tar.xz
-    rm mingw-w64-$arch-ca-certificates-20180409-1-any.pkg.tar.xz
-  condition: and(succeeded(), eq(variables['Agent.OS'], 'Windows_NT'))
-  displayName: Install working ca-certificates for msys
-
 # Make sure we use the native python interpreter instead of some msys equivalent
 # one way or another. The msys interpreters seem to have weird path conversions
 # baked in which break LLVM's build system one way or another, so let's use the