Clean up public interfaces

Clean up public interfaces

The Java programming language assigns certain defaults for methods
and constants defined in interfaces.  This change removes the
unnecessary redundant modifiers appropriately.

For example:
* interface methods are public by default
* interface constants are public by default
* interface methods are abstract unless "default" is specifically
  used (as of JDK8+).

This is really just to get rid of annoying warnings present in
IDE(s).

Issue-Id: SDNC-79
Change-Id: I2e6b3e4fa02bad1beee2cbb49d3766722eff1ba0
Signed-off-by: Ryan Goulding <ryandgoulding@gmail.com>