logging: disallow move construction/assignment for LogCategory
logging: disallow move construction/assignment for LogCategory

Summary:
LogCategory objects store pointers to their parent and sibling categories.  The
address of each LogCategory therefore matters, and we cannot allow moving them
to another address.

Explicitly delete the move constructor and assignment operator to ensure that
no-one ever accidentally tries to move a LogCategory object.

Reviewed By: yfeldblum

Differential Revision: D6893208

fbshipit-source-id: 32f36c5992e850cc6e90d02c7c74fb758e9f745b

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