arm64: mte: Remove unused mte_assign_mem_tag_range()

arm64: mte: Remove unused mte_assign_mem_tag_range()

mte_assign_mem_tag_range() was added in commit c80d45c42d37
("arm64: mte: add in-kernel MTE helpers") in 5.11 but moved out of
mte.S by commit 96aa5cfe8d5b ("arm64: kasan: simplify and inline
MTE functions") in 5.12 and renamed to mte_set_mem_tag_range().
96aa5cfe8d5b did not delete the old function prototypes in mte.h.

Remove the unused prototype from mte.h.

Cc: Will Deacon <will@kernel.org>
Reported-by: Derrick McKee <derrick.mckee@gmail.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lore.kernel.org/r/20210407133817.23053-1-vincenzo.frascino@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>