meson: gl: fix 'invalid keyword argument' meson warnings

Required is not a valid kwarg for cc.has_header()
diff --git a/ext/gl/meson.build b/ext/gl/meson.build
index 684a6cc..913c199 100644
--- a/ext/gl/meson.build
+++ b/ext/gl/meson.build
@@ -103,7 +103,7 @@
     optional_deps += bcm_host_dep
   endif
 
-  if egl_dep.found() and cc.has_header('libdrm/drm_fourcc.h', required : false)
+  if egl_dep.found() and cc.has_header('libdrm/drm_fourcc.h')
     optional_deps += allocators_dep
   endif
 
diff --git a/gst-libs/gst/gl/meson.build b/gst-libs/gst/gl/meson.build
index d9f8dfa..4ab5c57 100644
--- a/gst-libs/gst/gl/meson.build
+++ b/gst-libs/gst/gl/meson.build
@@ -283,7 +283,7 @@
       gl_dep = cc.find_library('GL', required : false)
     endif
 
-    if not cc.has_header('GL/gl.h', required : false)
+    if not cc.has_header('GL/gl.h')
       gl_dep = unneeded_dep
     endif
 
@@ -334,7 +334,7 @@
       gles2_dep = cc.find_library('GLESv2', required : false)
 #    endif
 
-     if not cc.has_header('GLES2/gl2.h', required : false)
+     if not cc.has_header('GLES2/gl2.h')
        gles2_dep = unneeded_dep
      endif
 
@@ -343,7 +343,7 @@
     endif
   endif
 
-  gles3_h = gles2_dep.found() and cc.has_header('GLES3/gl3.h', required : false, dependencies : gles2_dep)
+  gles3_h = gles2_dep.found() and cc.has_header('GLES3/gl3.h', dependencies : gles2_dep)
 
   gles_includes = '''
 #ifdef HAVE_IOS /* FIXME */
@@ -351,7 +351,7 @@
 # include <OpenGLES/ES2/glext.h>
 #else'''
   if gles3_h
-    gles3ext3_h = gles3_h and cc.has_header('GLES3/gl3ext.h', required : false, dependencies : gles2_dep)
+    gles3ext3_h = gles3_h and cc.has_header('GLES3/gl3ext.h', dependencies : gles2_dep)
     gles_includes += '''
 # include <GLES3/gl3.h>
 # include <GLES2/gl2ext.h>'''
@@ -440,7 +440,7 @@
     gl_platform_deps += egl_dep
     glconf.set10('GST_GL_HAVE_PLATFORM_EGL', 1)
 
-    if cc.has_header('libdrm/drm_fourcc.h', required : false)
+    if cc.has_header('libdrm/drm_fourcc.h')
       gl_misc_deps += allocators_dep
       glconf.set10('GST_GL_HAVE_DMABUF', 1)
     endif