[analyzer][NFC] Prune a very obsolete comment about CoreEngine (#101173)

Once upon a time, a long time (16 years) ago there were two classes
called `GREngineImpl` and `template <class CHECKER> GrEngine`. As the
years passed, they were merged into a single class that went through
several renames, but this comment still preserved the memory of their
old relationship... until now.

Author: NagyDonat

clang/include/clang/StaticAnalyzer/Core/PathSensitive/CoreEngine.h

@@ -45,14 +45,8 @@ class FunctionSummariesTy;
 class ExprEngine;
 
 //===----------------------------------------------------------------------===//
-/// CoreEngine - Implements the core logic of the graph-reachability
-///   analysis. It traverses the CFG and generates the ExplodedGraph.
-///   Program "states" are treated as opaque void pointers.
-///   The template class CoreEngine (which subclasses CoreEngine)
-///   provides the matching component to the engine that knows the actual types
-///   for states.  Note that this engine only dispatches to transfer functions
-///   at the statement and block-level.  The analyses themselves must implement
-///   any transfer function logic and the sub-expression level (if any).
+/// CoreEngine - Implements the core logic of the graph-reachability analysis.
+/// It traverses the CFG and generates the ExplodedGraph.
 class CoreEngine {
   friend class CommonNodeBuilder;
   friend class EndOfFunctionNodeBuilder;