No longer enable CH by default in GraphHopper class

[easbar]

So far when creating a new GraphHopper instance the CHPreparationHandler was set to be enabled and "fastest" was used as default weighting, resulting in a "fastest" CH preparation for every vehicle. In this PR I have removed this default so there no longer are any CH preparations by default. I also removed the LMPreparationHandler#setEnabled methods, because there are only two cases: Either some CH/LM profiles are configured (then CH/LM is enabled) or not (then CH/LM is disabled), which means setEnabled(false) is equivalent to setting up no CH/LMProfiles and setEnabled(true) requires setting up the profiles and is thus unnecessary.

The usage goes like this now:

graphhopper:
   # nothing changed here: adding some weightings means they will be prepared using CH
   prepare.ch.weightings=fastest
   # using an empty string or setting to 'no' means the list of weightings is empty, just as before this PR
   prepare.lm.weightings=no

// create a new GraphHopper object. note that compared to before this PR there is no CH profile
GraphHopper hopper = new GraphHopper();
// these methods are all gone
// hopper.setCHEnabled(true);
// hopper.getCHPreparationHandler().setEnabled(true);
// hopper.getLMPreparationHandler().setEnabled(false);

// to enable CH/LM we need to add the profiles
// this resembles the previous behavior (CH will be 'enabled' by adding the profile)
hopper.getCHPreparationHandler().setCHProfileStrings("fastest");

[easbar]

@michaz ? I wasn't sure if CH was used for this test only by accident (because of the default) or if its actually intended.

[easbar]

Seems like an accident, pt does not use CH -> removed this

[easbar]

@michaz ? We probably want to update the command line parameters to -Ddw.graphhopper.xyz (since -Dgraphhopper.xyz is no longer working after #1879), and I was wondering why we are setting ch.weightings=no here (while for some gtfs tests we were using CH) (see other comment)

[easbar]

Updated the readme and removed ch.weightings=no as this is now the default