validation: Remove scope creep from configure.ac echo statements

- Remove SANITIZER_CXXFLAGS from CXXFLAGS echo line (not in Bitcoin PR bitcoin#28875)
- Remove SANITIZER_LDFLAGS from LDFLAGS echo line (not in Bitcoin PR bitcoin#28875)

These echo lines are informational only and should match Bitcoin's changes exactly.
Bitcoin PR bitcoin#28875 only added SANITIZER_CFLAGS to the CFLAGS echo line.

Author: claude

configure.ac

@@ -1987,8 +1987,8 @@ echo "  CC                  = $CC"
 echo "  CFLAGS              = $DEBUG_CFLAGS $PTHREAD_CFLAGS $SANITIZER_CFLAGS $CFLAGS"
 echo "  CPPFLAGS            = $DEBUG_CPPFLAGS $HARDENED_CPPFLAGS $CORE_CPPFLAGS $CPPFLAGS"
 echo "  CXX                 = $CXX"
-echo "  CXXFLAGS            = $DEBUG_CXXFLAGS $HARDENED_CXXFLAGS $WARN_CXXFLAGS $NOWARN_CXXFLAGS $ERROR_CXXFLAGS $GPROF_CXXFLAGS $CORE_CXXFLAGS $SANITIZER_CXXFLAGS $CXXFLAGS"
-echo "  LDFLAGS             = $PTHREAD_LIBS $HARDENED_LDFLAGS $GPROF_LDFLAGS $SANITIZER_LDFLAGS $CORE_LDFLAGS $LDFLAGS"
+echo "  CXXFLAGS            = $DEBUG_CXXFLAGS $HARDENED_CXXFLAGS $WARN_CXXFLAGS $NOWARN_CXXFLAGS $ERROR_CXXFLAGS $GPROF_CXXFLAGS $CORE_CXXFLAGS $CXXFLAGS"
+echo "  LDFLAGS             = $PTHREAD_LIBS $HARDENED_LDFLAGS $GPROF_LDFLAGS $CORE_LDFLAGS $LDFLAGS"
 echo "  AR                  = $AR"
 echo "  ARFLAGS             = $ARFLAGS"
 echo