Change displayed trace descriptors

Descriptor before:
'Transitions (wm_transition_trace.winscope (bugreport.zip), shell_transition_trace.winscope (bugreport.zip))'

Descriptor after:
'wm_transition_trace.winscope (bugreport.zip), shell_transition_trace.winscope (bugreport.zip)'

Fix: b/285561971
Test: load trace and check the displayed descriptor
Change-Id: Ia96c58d563036c68e2d9ab428a94051a23a6a5b9