Removed code to clear text selection after copying text by the 'copy' menu of context...

Removed code to clear text selection after copying text by the 'copy' menu of context menu.

[Title] Removed code to clear text selection after copying text by the 'copy' menu of context menu.
[Issue#] N/A
[Problem] After copying text, caret disappear and IME is not hidden.
          So, user can not enter text in input field.
[Cause] There is code to clear text selection after copying text.
[Solution] Removed code to clear text selection like copy operation of native app.

Change-Id: I7c661662337bb34dd163fea6152bfdc837d66fa0