Removing wall under truss
The wall is not structural and the top plate tie-in is not structural if, 1) the trusses are tied to the remaining wall, 2) the top plate is spliced properly. 

1) Any lateral bracing that the wall could provide, can be taken by attaching the existing roof trusses to the top plate. I like using Simpson H-1 clips to tie the truss to the top plate. I like the H-1 because it provides lateral resistance and uplift resistance. 
See: https://www.strongtie.com/resources/product-installers-guide/h1-installation

2) The existing top plates need to be properly lapped (spliced), which now needs something like Simpson LSTI strap. I like the LSTI strap because it’s made for application on a single plate. See: https://www.homedepot.com/p/Simpson-Strong-Tie-LSTI-3-3-4-in-x-49-in-18-Gauge-Strap-Tie-LSTI49/205326016

The bottom plate extends past the wall, so provide a block at the top plate where the wall is removed and center the strap at the intersection of where the wall was located.