Replace underscores with spaces in DeletedContribs form

Replace underscores with spaces in DeletedContribs form

If you go to Special:Contributions/User_Foo and click on the link to
Special:DeletedContributions/User_Foo, the form field for selecting the
user is populated with the value "User_Foo", which isn't pretty to see.
Instead, let's replace underscores with spaces to directly show "User
Foo".

Change-Id: I2b144c9dbe41e2dd01bbb530dc5b43547fc4230f