Revert "[PixelOverlay] Thread part of FPP::MemoryMap::TextMessage()"

This reverts commit 45ac77e3f02cef9bfd1bc748657a697236be116b.

The Pi is taking too long to spin up a new thread in Perl so this change
needs to be reverted and redone to have a long-running thread.
[Network] Disable power management on wlan0 (again)