JBR-1929 Improve rendering of San Francisco font of macOS Catalina

Reverting gamma correction because of rendering artifacts in the light theme

This reverts commit 5016db51

(cherry picked from commit c1d644a004)

src/java.desktop/macosx/native/libawt_lwawt/font/CGGlyphImages.m

@@ -282,13 +282,7 @@ CGGI_CopyImageFromCanvasToRGBInfo(CGGI_GlyphCanvas *canvas, GlyphInfo *info)
 static inline UInt8
 CGGI_ConvertBWPixelToByteGray(UInt32 p)
 {
-    UInt8* lut = getReverseGammaLut();
-
-    UInt8 r = lut[0xFF - (p >> 24 & 0xFF)];
-    UInt8 g = lut[0xFF - (p >> 16 & 0xFF)];
-    UInt8 b = lut[0xFF - (p >>  8 & 0xFF)];
-
-    return ((r + g + b) / 3);
+    return 0xFF - (((p >> 24 & 0xFF) + (p >> 16 & 0xFF) + (p >> 8 & 0xFF)) / 3);
 }
 
 static void