Remove the hooks in RegionObserver which are designed to construct a StoreScanner which is marked as IA.Private

These methods are removed: KeyValueScanner preStoreScannerOpen(ObserverContext<RegionCoprocessorEnvironment> c,       Store store, Scan scan, NavigableSet<byte[]> targetCols, KeyValueScanner s, long readPt)       throws IOException; InternalScanner preFlushScannerOpen(ObserverContext<RegionCoprocessorEnvironment> c,       Store store, List<KeyValueScanner> scanners, InternalScanner s, long readPoint)       throws IOException; InternalScanner preCompactScannerOpen(ObserverContext<RegionCoprocessorEnvironment> c,       Store store, List<? extends KeyValueScanner> scanners, ScanType scanType, long earliestPutTs,       InternalScanner s, CompactionLifeCycleTracker tracker, CompactionRequest request,       long readPoint) throws IOException; For flush and compaction, CP users are expected to wrap the InternalScanner in preFlush/preCompact. And for normal region operation, just use preGetOp/preScannerOpen to modify the Get/Scan object. This method in Region interface is also removed as we do not need to use read point in CP hooks anymore: long getReadPoint(IsolationLevel isolationLevel);