Revert "Arm backend: Rerun duplicate-user fusion after TOSA lowering" (#21106)

Reverts pytorch/executorch#21041

This change breaks executorch/backends/arm/test:addmm
test_addmm_u55_INT[basic] on Corstone-300: the model output is all zeros
instead of the reference [[2,4],[6,8]].

Root cause: running FuseDuplicateUsersPass after InsertRescalePass. In
the
[basic] case x1 and x3 are value-identical, so FuseEqualPlaceholdersPass
merges them into a single placeholder that feeds both the matmul operand
and the bias/add path. After rescale insertion, that shared producer has
multiple tosa.RESCALE users, and fusing them corrupts the quantized
addmm
data flow, zeroing the output. Bisected to the late
FuseDuplicateUsersPass
insertion specifically (reordering EnsureUniqueOutputNodesPass is not
the
cause).

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218 @mansnils
@Sebastian-Larsson @robell @rascani