Remove --cpusampler.Mode, it has no effect with the new CPUSampler implementation

Author: eregon

doc/contributor/profiling.md

@@ -48,12 +48,9 @@ Creating the flame graph is a multi-stage process. First, we need to profile the
 with the JSON formatter:
 
 ```bash
-jt ruby --cpusampler --cpusampler.Mode=roots --cpusampler.Output=json -e 'p :hello' > simple-app.json
+jt ruby --cpusampler --cpusampler.Output=json -e 'p :hello' > simple-app.json
 ```
 
-The `--cpusampler.Mode=roots` option will sample roots, including inlined functions,
-which can often give a better idea of what is contributing to the overall method execution time.
-
 The JSON profiler formatter encodes call graph information that isn't available in the
 histogram format. To make a flame graph out of this output, however, we need to transform
 it into a format that folds the call stack samples into single lines. This can be done

spec/truffle/tools_spec.rb

@@ -68,7 +68,7 @@ def foo
       t.kill
       t.join
       RUBY
-      out = ruby_exe(code, options: "--cpusampler --cpusampler.Mode=roots")
+      out = ruby_exe(code, options: "--cpusampler")
       out.should.include?(":kill")
       out.should.include?("block in Object#foo")
       out.should_not.include?('KillException')

tool/jt.rb

@@ -38,7 +38,7 @@
 
 JDEBUG = '--vm.agentlib:jdwp=transport=dt_socket,server=y,address=8000,suspend=y'
 METRICS_REPS = Integer(ENV['TRUFFLERUBY_METRICS_REPS'] || 10)
-DEFAULT_PROFILE_OPTIONS = %w[--cpusampler --cpusampler.Mode=roots --cpusampler.Output=json]
+DEFAULT_PROFILE_OPTIONS = %w[--cpusampler --cpusampler.Output=json]
 
 RUBOCOP_INCLUDE_LIST = %w[
   lib/cext