package/monkey: bump to latest git commit

This will fix a build failure with gcc 10

- Update indentation in hash file (two spaces)
- Drop INSTALL_SYSCONFDIR, INSTALL_WEBROOTDIR and WITH_SYSTEM_MALLOC
  (not available since
  https://github.com/monkey/monkey/commit/df145932e33fca0d4a1dcd9d7675f996c8e6a73b)
- Set WITHOUT_HEADERS to ON because headers are not needed and to avoid
  the following build failure:

CMake Error at include/cmake_install.cmake:46 (file):
  file INSTALL cannot find
  "/home/fabrice/buildroot/output/build/monkey-f54856ce250c4e25735434dc75717a4b7fbfc45b/include/mk_core.h":
  No such file or directory.
Call Stack (most recent call first):
  cmake_install.cmake:69 (include)

Upstream is aware than the lack of release is an issue but no comments
since 2018: https://github.com/monkey/monkey/issues/276

Fixes:
 - http://autobuild.buildroot.org/results/0b723937ca048228082d040100f6e6324ac8300b



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>