Fix build with OpenEXR>=3

Index: cmake/FindIlmbase.cmake
--- cmake/FindIlmbase.cmake.orig
+++ cmake/FindIlmbase.cmake
@@ -12,9 +12,6 @@ find_library(ILMBASE_IEX_LIBRARY Iex)
 
 set(ILMBASE_LIBRARIES ${ILMBASE_IMATH_LIBRARY} ${ILMBASE_IEX_LIBRARY})
 
-file(STRINGS ${ILMBASE_INCLUDE_DIRS}/OpenEXR/IlmBaseConfig.h version_line
-     REGEX "ILMBASE_VERSION_STRING|PACKAGE_VERSION")
-string(REGEX MATCH "[0-9]+.[0-9]+.[0-9]+" ILMBASE_VERSION_STRING ${version_line})
 
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args(Ilmbase
