wscript: try to automatically set console subsystem flag depending on target features

Remove subsystem flag from shlibs and stlibs, it's only required for executables.

3rdparty/bzip2/wscript

@@ -29,6 +29,5 @@ def build(bld):
 		target = 'bzip2',
 #		use = 'bz_version.h',
 		includes = ['.', 'bzip2/'],
-		subsystem = bld.env.MSVC_SUBSYSTEM,
 		export_includes = ['bzip2/']
 	)

3rdparty/gl4es/wscript

@@ -19,5 +19,4 @@ def build(bld):
 		includes = ['gl4es/src', 'gl4es/src/gl', 'gl4es/src/glx', 'gl4es/include'],
 		defines  = ['NOX11', 'NO_GBM', 'NO_INIT_CONSTRUCTOR', 'DEFAULT_ES=2', 'NOEGL', 'NO_LOADER', 'STATICLIB'],
 		cflags   = ['-w', '-fvisibility=hidden', '-std=gnu99'],
-		subsystem = bld.env.MSVC_SUBSYSTEM,
 		export_includes = '.')

3rdparty/opus/wscript

@@ -64,6 +64,5 @@ def build(bld):
 		features = 'c',
 		includes = includes,
 		defines = defines,
-		subsystem = bld.env.MSVC_SUBSYSTEM,
 		export_includes = ['opus/include/']
 	)