Remove deprecated CASTOR support

cmake/modules/FindCastor.cmake

cmake/modules/RootBuildOptions.cmake

cmake/modules/RootConfiguration.cmake

cmake/modules/SearchInstalledSoftware.cmake

config/Makefile.in

config/rootrc.in

core/base/src/TUrl.cxx

documentation/doxygen/Doxyfile

etc/plugins/TFile/P030_TCastorFile.C

gui/sessionviewer/src/TSessionDialogs.cxx

io/CMakeLists.txt

io/castor/CMakeLists.txt

io/castor/doc/index.txt

io/castor/inc/LinkDef.h

io/castor/inc/TCastorFile.h

io/castor/src/TCastorFile.cxx

io/io/src/TFile.cxx

tree/tree/src/TBranch.cxx