Remove BTM_SCO_INCLUDED flag

* Instead of removing SCO related code during compilation, platforms
  should chose not to call SCO related methods when SCO is not supported
* For example, platforms can choose to not initialize HFP to avoid using
  SCO commands
* This CL removes BTM_SCO_INCLUDED compile time flag to simplify code
  flow and improve readability

Bug: 122279647
Test: mm -j40; run Bluetooth stack and make phone call
Change-Id: I67d290839091f66c289a428496304c8b3e1dbe21