Build/Test Tools: Remove Internet Explorer 11 from the browserslist.

This officially removes support for Internet Explorer 11 in the CSS files run through the build process in Core.

Individual tickets should be opened for removing each manually maintained area of the code base targeting IE11.

The resulting changes to CSS files are included in this commit.

Fixes #53077.

git-svn-id: https://develop.svn.wordpress.org/trunk@50784 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/css/common.css

@@ -2128,7 +2128,6 @@ html.wp-toolbar {
 .postbox .hndle,
 .stuffbox .hndle {
 	-webkit-user-select: none;
-	-ms-user-select: none;
 	user-select: none;
 }
 
@@ -3520,7 +3519,6 @@ img {
 	border-left: 1px solid #dcdcde;
 	border-right: 1px solid #dcdcde;
 	-webkit-user-select: none;
-	-ms-user-select: none;
 	user-select: none;
 }
 
@@ -3752,10 +3750,6 @@ img {
 
 }
 
-@-ms-viewport {
-	width: device-width;
-}
-
 @media screen and (max-width: 782px) {
 	html.wp-toolbar {
 		padding-top: 46px;