DEV-38598, QAR-1619: Ensure we remove LLFloaterTOS from LLFloaterReg registry.

LLFloater's destructor calls LLFloaterReg::removeInstance() with its own name
and key. But for the new LLFloaterTOS invocation, we pass a key that's an LLSD
map. removeInstance() critically depends on LLFloater::KeyCompare::equate() --
but equate() never considered a non-scalar LLSD key value. Fortunately
llsdutil.h already provides a deep-equality function for LLSD: llsd_equals().
Making equate() trivially call llsd_equals() fixes the crash on TOS cancel.