build-sys: Remove unused libstoragemgmt references

The daemon does not need libstoragemgmt, so we don't need to reference
libstoragemgmt.la or its CFLAGS in daemon/Makefile.am
daemon: Use per-target CFLAGS

Currently, CPPFLAGS are set globally for both lsmd and lsm_restd through
the use of AM_CPPFLAGS. However, lsmd does not need any such flags, they
are only needed by lsm_restd. This commit moves the global AM_CPPFLAGS
to lsm_restd_CFLAGS. It also removes LIBGLIB_CFLAGS as glib is not used
here.
c_binding: Remove unused Makefile.am variable

DEPS is not the name of an automake variable (closest name would be
DEPENDENCIES, see
https://www.gnu.org/software/automake/manual/html_node/Variable-Index.html#Variable-Index
). Moreover nothing uses DEPS in the Makefile.am or in other build
system files so it can be removed.
build-sys: Use automake 'subdir-objects' options

c_binding/Makefile.am references some files from the util/ subdirectory.
This causes warning with newer automakes unless 'subdir-objects' is
used:

c_binding/Makefile.am:12: warning: source file 'util/qparams.c' is in a subdirectory,
c_binding/Makefile.am:12: but option 'subdir-objects' is disabled
automake: warning: possible forward-incompatibility.
automake: At least a source file is in a subdirectory, but the 'subdir-objects'
automake: automake option hasn't been enabled.  For now, the corresponding output
automake: object file(s) will be placed in the top-level directory.  However,
automake: this behaviour will change in future Automake versions: they will
automake: unconditionally cause object files to be placed in the same subdirectory
automake: of the corresponding sources.
automake: You are advised to start using 'subdir-objects' option throughout your
automake: project, to avoid future incompatibilities.
c_binding: Fix small typo in API doc

"fils system" -> "file system"
daemon: Don't use deprecated json_object_object_get

This causes a warning on fedora 21 as this has been deprecated.
This commit switches to the recommended json_object_object_get_ex
replacement.
This function has been available since at least json-c 0.10 which is
the minimum version we require, so we don't need a fallback
version of that function.
daemon: Remove obsolete build comments

The compilation instructions are no longer needed as the rest daemon
build is integrated in the main autotools-based build system.
daemon: Remove unused #define

The MHD_PLATFORM_H #define needs to be set before including
microhttpd.h, so it had no effect where it was placed.
This #define is useful when building on systems where the standard
headers defining uint64_t, size_t, ... are not available.
As we are building on reasonably standard platforms, we can rely let
microhttpd.h use the standard headers.
daemon: Mark internal functions as 'static'