Remove obsolete TODOs

TODO

 # ToDo
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 ## Bugs
 These issues are not real bugs, but unexpected behaviour that might
 lead to serious trouble if you're not aware of.
@@ -13,8 +11,6 @@ lead to serious trouble if you're not aware of.
 * MultigridStep is not robust wrt setup order.
 * MultigridStep deletes the ignoreNodes_ when calling preprocess() a second time
 
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 ## Performance issues
 While a suboptimal implementation might be OK, if it is cleaner
 and more readable these issues may decrease the performance
@@ -29,8 +25,6 @@ without any again.
   be OK but much cheaper. (Does this have any performance impact on
   linear elasticity problems?)
 
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 ## Design issues
 Things that could be improved to make dune-solvers easier to use, understand,
 and maintain.
@@ -43,8 +37,6 @@ and maintain.
   store the solution there and make getSol() return this reference
   and no copy.
   (C: I'd prefer the latter to reduce the number of vector copies).
-* Remove deprecated methods MultigridStep::setNumberOfLevels(), setProblem(...,numlevels)
-  constructors with argument numlevels after next release (2.3)
 * Make setting up a MultigridStep easier. E.g. by providing a default
   version that is preconfigured with GS smoother and coarse grid solver.
 * MultigridStep works differently on the finest and the other
@@ -61,18 +53,13 @@ and maintain.
   Solver Base-classes (Solver, IterativeSolver, LoopSolver atl) and substitute the 
   q&d version implemented now
 
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 ## Naming of classes and members
 
 * ignoreNodes_ should be called ignore_/ignoreIndices_/ignoreComponents_
 
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 ## Missing features
 A wish list for features that would be very welcome.
 
 * Transfer operator assembler for adaptively refined grids (without refinementtype=copy)
   This is already implemented in dune-fufem. It could be moved here if the
   dependency on P1NodalBasis is removed.
-* An interface to add custom output and termination criteria to the LoopSolver. 
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