No duplicate line in gfa out
If we have a duplicate line in paf we produce a duplicate line in gfa, some gfa parser can't deal with this.
For this paf :
A 1000 200 1000 + B 1000 0 800
A 1000 200 1000 + B 1000 0 800
B 1000 0 800 + A 1000 200 1000
produce this gfa:
S A * LN:i:1000
S B * LN:i:1000
L A + B + 800M NM:i:0 om:f:0.00 # No duplication of this line