[lldb][NFCI] Remove BreakpointIDList::InsertStringArray (#77161)

This abstraction is leaky and BreakpointIDList does not need to know
about CommandReturnObject.
Additionally, setting the CommandReturnObject inout param to a success
state does very little. The function returns immediately if the input
ArrayRef is empty, and reading
CommandObjectMultiwordBreakpoint::VerifyIDs more closely, the input is
always empty if the previous call to
BreakpointIDList::FindAndReplaceIDRanges failed. If the call was
successful, then the CommandReturnObject is already in a success state.

I have opted to remove the function altogether and inline the
functionality where it was used.