Simplify the code
Simplify the code

window.localStorage.getItem already returns a value of type string|null,
the only time the typeof check would be false is on `null` value,
assigning which to this.recordTargetOS is done anyway on a separate
line.

Change-Id: Ia5a1ddd5ede42f7552a4ad38cdbe02345f177cbc
google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto,google/perfetto