Remove unneeded header decl of move_opcode_tuple
Remove unneeded header decl of move_opcode_tuple

Summary:
It's only used in InstructionSelection.cpp and anywhere else that
header is included it causes an unused function warning.

Reviewed By: minjang

Differential Revision: D5864878

fbshipit-source-id: ff5c44fbbbe55cefb602f33a30bde8f42a46f447

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