Remove mail blockquote special case handling.

LayoutTests/platform/chromium-win/editing/pasteboard/merge-end-blockquote-expected.txt

-EDITING DELEGATE: shouldBeginEditingInDOMRange:range from 0 of DIV > BODY > HTML > #document to 1 of DIV > BODY > HTML > #document
-EDITING DELEGATE: webViewDidBeginEditing:WebViewDidBeginEditingNotification
-EDITING DELEGATE: webViewDidChangeSelection:WebViewDidChangeSelectionNotification
-EDITING DELEGATE: shouldChangeSelectedDOMRange:range from 17 of #text > DIV > BODY > HTML > #document to 17 of #text > DIV > BODY > HTML > #document toDOMRange:range from 16 of #text > DIV > BODY > HTML > #document to 16 of #text > DIV > BODY > HTML > #document affinity:NSSelectionAffinityDownstream stillSelecting:FALSE
-EDITING DELEGATE: webViewDidChangeSelection:WebViewDidChangeSelectionNotification
-EDITING DELEGATE: webViewDidChange:WebViewDidChangeNotification
-EDITING DELEGATE: shouldEndEditingInDOMRange:range from 0 of DIV > BODY > HTML > #document to 1 of DIV > BODY > HTML > #document
-EDITING DELEGATE: webViewDidEndEditing:WebViewDidEndEditingNotification
-EDITING DELEGATE: shouldBeginEditingInDOMRange:range from 0 of DIV > BODY > HTML > #document to 1 of DIV > BODY > HTML > #document
-EDITING DELEGATE: webViewDidBeginEditing:WebViewDidBeginEditingNotification
-EDITING DELEGATE: webViewDidChangeSelection:WebViewDidChangeSelectionNotification
-EDITING DELEGATE: webViewDidChangeSelection:WebViewDidChangeSelectionNotification
-EDITING DELEGATE: webViewDidChangeSelection:WebViewDidChangeSelectionNotification
-EDITING DELEGATE: shouldChangeSelectedDOMRange:range from 14 of #text > DIV > BLOCKQUOTE > DIV > BODY > HTML > #document to 14 of #text > DIV > BLOCKQUOTE > DIV > BODY > HTML > #document toDOMRange:range from 3 of #text > DIV > BLOCKQUOTE > DIV > BODY > HTML > #document to 3 of #text > DIV > BLOCKQUOTE > DIV > BODY > HTML > #document affinity:NSSelectionAffinityDownstream stillSelecting:FALSE
-EDITING DELEGATE: webViewDidChangeSelection:WebViewDidChangeSelectionNotification
-EDITING DELEGATE: webViewDidChange:WebViewDidChangeNotification
-layer at (0,0) size 800x600
-  RenderView at (0,0) size 800x600
-layer at (0,0) size 800x600
-  RenderBlock {HTML} at (0,0) size 800x600
-    RenderBody {BODY} at (8,8) size 784x576
-      RenderBlock {P} at (0,0) size 784x20
-        RenderText {#text} at (0,0) size 582x19
-          text run at (0,0) width 383: "This tests pasting a Mail blockquote at the start of a paragraph. "
-          text run at (383,0) width 199: "Blockquoting should be stripped."
-      RenderBlock {DIV} at (0,36) size 784x20
-        RenderText {#text} at (0,0) size 116x19
-          text run at (0,0) width 116: "Blockquoted Textx"
-      RenderBlock {P} at (0,72) size 784x40
-        RenderText {#text} at (0,0) size 782x39
-          text run at (0,0) width 276: "This tests pasting text into a Mail blockquote. "
-          text run at (276,0) width 506: "The last bit of content in the incoming fragment should be merged with the paragraph"
-          text run at (0,20) width 210: "after the position being pasted into."
-      RenderBlock {DIV} at (0,128) size 784x56
-        RenderBlock {BLOCKQUOTE} at (40,0) size 704x20
-          RenderBlock {DIV} at (0,0) size 704x20
-            RenderText {#text} at (0,0) size 98x19
-              text run at (0,0) width 98: "Blockquotedfoo"
-        RenderBlock (anonymous) at (0,36) size 784x0
-        RenderBlock {BLOCKQUOTE} at (40,36) size 704x20
-          RenderBlock {DIV} at (0,0) size 704x20
-            RenderText {#text} at (0,0) size 47x19
-              text run at (0,0) width 47: "barText"
-caret: position 3 of child 0 {#text} of child 0 {DIV} of child 1 {BLOCKQUOTE} of child 10 {DIV} of body