Is the camera apk in the correct folder with correct permissions?
Permissions should be rw-r--r-- (have a look at other apps in the same folder and copy their permissions).
Once you've done that reboot to recovery and clear Cache and Dalvik.
Here's the correct locations for the two different cameras:
New Google camera (com.google.android.Googlecamera-1.apk) = /data/app/
Older "standard" camera (camera2.apk) = /system/app/
Also make sure no traces of the Sony camera are left... check through your folder
Not saying it will 100% work, but worth a try if nothing else does!
Main Device: Google Nexus 5
Other Devices: Samsung Galaxy Note 2, Samsung Galaxy Tab 2 10.1, Samsung Galaxy S2, Motorola Moto G
Retired: HTC Hero, HTC Wildfire S, HTC Desire HD, Samsung Galaxy Note 1
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