Remove IE specific code from Twenty Seventeen. Remove custom IE stylesheet contents, the HTML5 shiv contents (also targeting Safari 4.x and Firefox 3.x), and IE-specific code. Props desrosj, sabernhardt, neychok, joedolson. Fixes #58836. Built from https://develop.svn.wordpress.org/trunk@60966 git-svn-id: http://core.svn.wordpress.org/trunk@60302 1a063a9b-81f0-0310-95a4-ce76da25c4cd