Remove dead code (unused functions, imports, args, locals)

[riasc]

From a Python audit. All grep-confirmed to have zero callers/readers.

• file_linecounter — unused function. segmeter/utility.py:9
• det_rightmost_start — unused method. segmeter/simulator.py:92
• update_leftgap — unused method. segmeter/simulator.py:82
• close_datafiles_complex — unused; only iterates the always-empty queries-complex. segmeter/simulator.py:146
• import calls — never referenced. segmeter/benchmark.py:6
• query_time / query_precision / query_memory = {} — all reassigned before any read. segmeter/benchmark.py:13-15
• self.intvls = {} — never read. segmeter/simulator.py:21
• from intervaltree import ... Interval — Interval unused. segmeter/tools/intersect_intervaltree.py:5
• --format / --stats args parsed but never read. segmeter/tools/intersect_intervaltree.py:76-79
• get_query_group datatype=="complex" branch — only ever called with "basic". segmeter/utility.py:54