remove lineHeight getter

Nothing is using it and we can add it back once the need arises.

src/editor-view.coffee

@@ -758,16 +758,6 @@ class EditorView extends View
     @css('line-height', lineHeight)
     @redraw()
 
-  # Public: Gets the line height for the editor
-  #
-  # Note that this is different from `lineHeight`, which is the computed
-  # height of a line using the bounding box.  This is the property value of
-  # CSS `line-height`.
-  #
-  # Returns a {Float} identifying the CSS line-height.
-  getLineHeight: ->
-    parseFloat(@css('line-height'))
-
   # Public: Redraw the editor
   redraw: ->
     return unless @hasParent()