[mlir][aarch64] Remove LIT config for lli (#89545)

This change will only affect MLIR integration tests to be run on
AArch64. When originally introduced, these tests would run with `lli`.
Those tests has since been updated to use `mlir-cpu-runner` instead, see
e.g.:

  * https://reviews.llvm.org/D155405
  * https://reviews.llvm.org/D146917

This patch removes all the leftover `lli` configuration in LIT that's
currently not needed (and is unlikely to be needed any time soon).