bt: use delete ctor instead of DISALLOW_COPY_AND_ASSIGN

Chromium now follows Google C++ styleguide (crbug/1010217).
DISALLOW_COPY_AND_ASSIGN will be deprecated, and delete the copy
copy constructors and assign operators instead explicitly is recommended.

Bug: 190446478
Tag: #floss
Test: FEATURES=test emerge-zork-floss floss

Change-Id: Ic268aa8fee941dd66d1857dae73a6b4b40c34979