Remove obsolete code in `DEBUG_MEM*` sections

[dschlaep]

DEBUG_MEM* sections of the SOILWAT2 code look like obsolete code – corresponding functionality (see comment at start of "mymemory.ch" has likely been replaced by third-party leak/memory analyzers (e.g., ASAN, leaks, valgrind)

DEBUG_MEM and DEBUG_MEM_X are currently not functional; the following all cause compilation errors

• make clean bin_run CPPFLAGS="-DDEBUG"
• make clean bin_run CPPFLAGS="-DDEBUG -DDEBUG_MEM"
• make clean bin_run CPPFLAGS="-DDEBUG_MEM"
• make clean bin_run CPPFLAGS="-DDEBUG -DDEBUG_MEM_X"
• make clean bin_run CPPFLAGS="-DDEBUG_MEM_X"

The following is functional

• make clean bin_run CPPFLAGS="-DSWDEBUG -DDEBUG_MEM_LOG"

--> Consider if we can remove these obsolete code sections to increase code maintainability and ease for future developments.

[dschlaep]

STEPWAT2 has not been utilizing "DEBUG_MEM" -- we have to go ahead to remove associated code.