Fix unneeded read in trace_parser

[ammrat13]

The parse_from_string method in trace_parser.cc currently reads in one delta for each active thread. However, tracer_tool.cu does not write the delta for the first thread since it will always be zero. This commit updates the behavior of trace_parser to match the intended trace format.

Even though this bug was present, it had no effect in the past since the base_delta_decompress function is correct.

[William-An]

@JRPan @tgrogers For the Jenkins test cases, do we only get traces with stride memory pattern? Looks like his original modification that removes the base_delta_compress call should either crash or generate invalid results for the simulator.

[tgrogers]

@ammrat13 - thanks for the commit.
Did you have a use case where you saw this bug having an effect?

@William-An, I am not sure we have all kinds of workloads with varying amounts of divergence in memory. However, the long tests are only looking at the uBenches which are probably almost always strided in their memory accesses.

https://tgrogers-pc01.ecn.purdue.edu/github-ci/accel-sim/correl/git_refs/pull/162/merge_139_1/l1readaccess.QV100-SASS-accel-6c0707c-gpgpu-68e1cd3.per-kernel.html

These look great - but it would be good to also correlate rodinia-3.1 I think so we get some more variety.
@JRPan - how much longer would it take to correlate the 3.1 apps alongside the uBench in the long tests?