build: Drop Visual Studio projects

In master, it is already possible to build GLib using Visual Studio
using Meson[1] for some time, so we should focus on maintaining only the
Meson build files for building GLib with Visual Studio.

[1]: There are caveats when building with Visual Studio 2008, namely
     that one needs to use the mt command to embed the manifests that
     are generated with the .exe/DLLs, for all builds, and that in the
     case where the compilation hangs on Visual Studio 2008 x64, as a
     workaround, should stop the build by terminating all cl.exe tasks
     and change the compiler optimization flag from /O2 (full speed) to
     /O1 (optimize for size), due to compiler optimization issues.

Makefile.am

@@ -7,7 +7,7 @@ include $(top_srcdir)/glib.mk
 ACLOCAL_AMFLAGS = -I m4macros ${ACLOCAL_FLAGS}
 
 SUBDIRS = . m4macros glib gmodule gthread gobject gio po docs tests subprojects
-DIST_SUBDIRS = $(SUBDIRS) build win32
+DIST_SUBDIRS = $(SUBDIRS) build
 
 bin_SCRIPTS = glib-gettextize
 
@@ -50,7 +50,6 @@ EXTRA_DIST += 			\
 	tap-driver.sh		\
 	tap-test		\
 	msvc_recommended_pragmas.h \
-	config.h.win32.in	\
         po/po2tbl.sed.in        \
 	glib-2.0.pc.in 		\
 	gobject-2.0.pc.in 	\
@@ -113,7 +112,6 @@ BUILT_EXTRA_DIST += 		\
 	README			\
 	INSTALL			\
 	ChangeLog		\
-	config.h.win32		\
 	$(NULL)
 
 CONFIGURE_DEPENDENCIES = acglib.m4