ci/android: Keep the LLVM install when rebuilding

Previously, when rebuilding LLVM for Android, the script would delete the
freshly built LLVM install. This caused the android_build container to
lack LLVM unless the container was rebuilt again, this time without
rebuilding LLVM, and instead just downloading the tarball.

Signed-off-by: Valentine Burley <valentine.burley@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34180>

.gitlab-ci/container/build-android-x86_64-llvm.sh

@@ -118,6 +118,4 @@ if [ -n "$CI" ]; then
   rm "${ANDROID_LLVM_ARTIFACT_NAME}.tar.zst"
 fi
 
-rm -rf "$LLVM_INSTALL_PREFIX"
-
 apt-get purge -y "${EPHEMERAL[@]}"