[Linaro:ARM_CI] Remove possible flaky test from skip list.
This change was included in https://github.com/tensorflow/tensorflow/pull/61522/commits/d23d49462965530c393e6a2a99efc9950eab63b9 so this PR is now moot.
//tensorflow/python/kernel_tests/nn_ops:atrous_conv2d_test was put on the skip list for being flaky. Remove it now to check current status.