Always reduce `count` when removing items from SimpleHashTable
Always reduce `count` when removing items from SimpleHashTable

In particlar `MapAndRemoveIf` used to not reduce `count`. That could cause the table to be larger than necessary in the long term.
It was also inflating the count of pinned references as reported in OOM postmotems.

Fixes: OS: #18369725

Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore