Remove ': overview' in span.title

It looks ugly, was not displayed to the user until the previous commit
(a51b61541f) and we'll have the same problem for the upcoming download
pages.

wiki/src/install/debian/usb-overview.html

-[[!meta title="Install from Debian, Ubuntu, or Mint: overview"]]
+[[!meta title="Install from Debian, Ubuntu, or Mint"]]
 
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]

wiki/src/install/expert/usb-overview.html

-[[!meta title="Install from Debian, Ubuntu, or Mint using the command line and GnuPG: overview"]]
+[[!meta title="Install from Debian, Ubuntu, or Mint using the command line and GnuPG"]]
 
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]

wiki/src/install/linux/usb-overview.html

-[[!meta title="Install from Linux: overview"]]
+[[!meta title="Install from Linux"]]
 
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]

wiki/src/install/mac/dvd-overview.html

-[[!meta title="Install from Mac by burning a DVD first: overview"]]
+[[!meta title="Install from Mac by burning a DVD first"]]
 
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]

wiki/src/install/mac/usb-overview.html

-[[!meta title="Install from Mac using the command line: overview"]]
+[[!meta title="Install from Mac using the command line"]]
 
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]

wiki/src/install/win/usb-overview.html

-[[!meta title="Install from Windows: overview"]]
+[[!meta title="Install from Windows"]]
 
 [[!meta stylesheet="bootstrap.min" rel="stylesheet" title=""]]
 [[!meta stylesheet="inc/stylesheets/assistant" rel="stylesheet" title=""]]