[lldb] Revive shell test after updating UnwindTable (#86770)

In
     commit 2f63718f
     Author: Jason Molenda <jmolenda@apple.com>
     Date:   Tue Mar 26 09:07:15 2024 -0700

[lldb] Don't clear a Module's UnwindTable when adding a SymbolFile
(#86603)

I stopped clearing a Module's UnwindTable when we add a SymbolFile to
avoid the memory management problems with adding a symbol file
asynchronously while the UnwindTable is being accessed on another
thread. This broke the target-symbols-add-unwind.test shell test on
Linux which removes the DWARF debub_frame section from a binary, loads
it, then loads the unstripped binary with the DWARF debug_frame section
and checks that the UnwindPlans for a function include debug_frame.

I originally decided that I was willing to sacrifice the possiblity of
additional unwind sources from a symbol file because we rely on assembly
emulation so heavily, they're rarely critical. But there are targets
where we we don't have...