ringtools/imy: fix duplicate definition of tdma_durations[] The bug was reported by Vadim Yanitskiy <fixeria@osmocom.org>, although the present fix is slightly different from the contributed patch: because main.c doesn't need this tdma_durations[] array at all, let's simply remove the reference to this array from main.c rather than turn it into an extern. I no longer remember my original thought flow that resulted (by mistake) in tdma_durations[] being multiply defined in main.c and durations.c. My intent might have been to define all globals in main.c and have the reference in durations.c be an extern - and I missed that extern - but without clear memory, I have no certainty. In any case, having this data array defined in the same module that fills it (durations.c) is sensible, so let's make it the new way.

# This PWT test melody is a subset of rising-chrom.pwt,
# reduced to just "white key" notes.

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