LE scanner BTA layer simplification

BTA layer for scanner is very complicated. This patch simplifies it:
* get rid of type redeclarations for BTM types
* get rid of trivial *_act methods and call BTM API directly where possible

Bug: 30622771
Test: slra FilterTest
Change-Id: I3899b30074b2abc4a3945c5cc14f1bb40a504876