floss: Update TODOs

* Added b/200066804 for LE Scanning API
* Added b/200065274 for restricted services/chars
* Added b/200070162 for concurrent write characteristic
* Removed a completed TODO in BtifGattClientCallbacks

Bug: 193685325
Tag: #floss
Test: Build

Change-Id: I33f93326f3bf07c18edafbc21ff1d48f05319fb0