Replace ":strings" with "strings"

It looks like this is a typo and can cause parse errors with some xml
deserialization libraries.

Test: manual - set User Control Disabled Packages - restart device -
confirm that policy is still set
Bug: 291711966

Change-Id: Ib8eb2356ece3d9f0e85b7b8c455e58106a1d84f1
1 file changed