Removing populate-secpected-screenshots.sh script since it's no longer needed.

tests/PHPUnit/populate-expected-screenshots.sh

-#!/bin/bash
-
-current_branch=$(git rev-parse --abbrev-ref HEAD)
-
-# checkout branch and missing files/directories/links if needed
-if ! git checkout $1; then
-    echo "failed to checkout branch, aborting"
-    exit 1
-fi
-
-test_files="UI/UIIntegrationTest.php
-Fixtures/ManySitesImportedLogsWithXssAttempts.php
-proxy/libs
-proxy/plugins
-proxy/tests"
-
-for file in $test_files
-do
-    if [ ! -e "$file" ]; then
-        git checkout master "$file"
-    fi
-done
-
-# run UI tests
-echo "Running UI tests..."
-phpunit UI &> /dev/null
-
-# copy processed png
-echo "Copying to expected screenshot dir..."
-if [ ! -d "UI/expected-ui-screenshots" ]; then
-    mkdir UI/expected-ui-screenshots
-fi
-
-cp UI/processed-ui-screenshots/* UI/expected-ui-screenshots
-
-# go back to original branch
-rm populate-expected-screenshots.sh
-git reset --hard
-git checkout $current_branch
-