unneeded -DUSE_MMAP in JDK native libs builds

[Baesken, Matthias]

Hello I noticed that   -DUSE_MMAP  is set for these  JDK native libs, but I cannot find it in the code   (for libzip it is different there the flag shows up in the code too ) :

Lib-jdk.jdi.gmk  :

32  $(eval $(call SetupJdkLibrary, BUILD_LIBDT_SHMEM, \
......
35 CFLAGS := $(CFLAGS_JDKLIB) -DUSE_MMAP, \


Lib-jdk.jdwp.agent.gmk :

30 $(eval $(call SetupJdkLibrary, BUILD_LIBDT_SOCKET, \
......
33 CFLAGS := $(CFLAGS_JDKLIB) -DUSE_MMAP \


Any objections  to remove those  2    -DUSE_MMAP    settings ?
If it is fine to remove I would prepare a  webrev .

Thanks, Matthias