Revert "Pass thread name as extra in gdbserver"

This reverts commit a1858de2f9a585d345c810287ddd9f18e50fd965.
Revert "Update to Google's 7.6 gdbserver"

This reverts commit 3e736c1c53710c894a3dab742ce335b02d3dc6c9.
Build 7.3 version of gdbserver to match Google's default