fix(benchmark): delete unneccessary, confusing code in loop

p.diags() is uninteresting inside the benchmark loop as p isn't touched
in the loop. Rather, diags is the relevant variable. However, diags and
its allocator (memory) are created and destroyed inside the benchmark
loop, so explicit clearing (diags.clear()) is unnecessary

Delete the clearing of p.diags().

Author: strager

benchmark/benchmark-lint.cpp

@@ -46,10 +46,6 @@ void benchmark_lint(benchmark::State &state) {
     Diag_List diags(&memory);
     Variable_Analyzer l(&diags, &config.globals(), var_options);
     visitor.copy_into(l);
-
-    // FIXME(strager): This does not deallocate memory. Memory usage will grow
-    // and grow and grow.
-    p.diags().clear();
   }
 }
 BENCHMARK(benchmark_lint);