Wayland: Remove superfluous global struct member

It seems unlikely that strlen will be a bottleneck when sending
clipboard contents.

src/wl_platform.h

@@ -308,7 +308,6 @@ typedef struct _GLFWlibraryWayland
     char*                       clipboardString;
     size_t                      clipboardSize;
     char*                       clipboardSendString;
-    size_t                      clipboardSendSize;
     int                         timerfd;
     short int                   keycodes[256];
     short int                   scancodes[GLFW_KEY_LAST + 1];

src/wl_window.c

@@ -1592,7 +1592,7 @@ static void dataSourceHandleSend(void* data,
                                  int fd)
 {
     const char* string = _glfw.wl.clipboardSendString;
-    size_t len = _glfw.wl.clipboardSendSize;
+    size_t len = strlen(string);
     int ret;
 
     if (_glfw.wl.dataSource != dataSource)
@@ -1675,7 +1675,6 @@ void _glfwSetClipboardStringWayland(const char* string)
     _glfw_free(_glfw.wl.clipboardSendString);
     _glfw.wl.clipboardSendString = copy;
 
-    _glfw.wl.clipboardSendSize = strlen(_glfw.wl.clipboardSendString);
     _glfw.wl.dataSource =
         wl_data_device_manager_create_data_source(_glfw.wl.dataDeviceManager);
     if (!_glfw.wl.dataSource)