[Script] Remove final modifier from private methods

* Private methods should not be declared final as there is no way to
  override them
* In Java there is no C++ 'const' like method modifiers that mark a
  method as not modifying the instance content
* Run 'private' method declared 'final' inspection in Intellij and
  accept automatic fixes to remove the modifier

Bug: 63597465
Test: make checkbuild, no manual changes, no functional changes
Change-Id: I57fb646ac592adc0fac36ec7d2552d63a96d239e