That is a custom function of the camera that can be change back to default with ease. While in one of the creative zones press the menu button and navigate to the 5th and final tab on the top right.
This is the Setup menu 2. In this menu, select “Custom Functions (C. Fn)” . This will open a submenu of numbered options. Select #04 and set it to 0: the default AF/AE lock on a half depress of the shutter.
That should get your camera back to the expected auto focus with the shutter button.