patch 8.1.1531: clipboard type name is inconsistent

Problem:    Clipboard type name is inconsistent.
Solution:   Rename VimClipboard to Clipboard_T.
diff --git a/src/proto/ops.pro b/src/proto/ops.pro
index 01df56f..0ff27a2 100644
--- a/src/proto/ops.pro
+++ b/src/proto/ops.pro
@@ -53,10 +53,10 @@
 void handle_viminfo_register(garray_T *values, int force);
 void write_viminfo_registers(FILE *fp);
 void x11_export_final_selection(void);
-void clip_free_selection(VimClipboard *cbd);
-void clip_get_selection(VimClipboard *cbd);
-void clip_yank_selection(int type, char_u *str, long len, VimClipboard *cbd);
-int clip_convert_selection(char_u **str, long_u *len, VimClipboard *cbd);
+void clip_free_selection(Clipboard_T *cbd);
+void clip_get_selection(Clipboard_T *cbd);
+void clip_yank_selection(int type, char_u *str, long len, Clipboard_T *cbd);
+int clip_convert_selection(char_u **str, long_u *len, Clipboard_T *cbd);
 void dnd_yank_drag_data(char_u *str, long len);
 char_u get_reg_type(int regname, long *reglen);
 char_u *get_reg_contents(int regname, int flags);