patch 9.1.2081: MS-Windows: unnecessary "#ifdef FEAT_GUI" in os_win32.c

patch 9.1.2081: MS-Windows: unnecessary "#ifdef FEAT_GUI" in os_win32.c

Problem:  MS-Windows: "#ifdef FEAT_GUI" exists within "ifdef
          FEAT_GUI_MSWIN", which is confusing when reading the code.
          FEAT_GUI is always defined if FEAT_GUI_MSWIN is defined (see
          vim.h).  Therefore, this check and the else block are
          unnecessary.
Solution: Removed unnecessary "#ifdef FEAT_GUI" (Muraoka Taro).

closes: #19164

Signed-off-by: Muraoka Taro <koron.kaoriya@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>