Improve strings for "Show Desktop" effects

Summary:
Problems with the current strings:
- Incorrect capitalization
- Grammatical errors ("to show the latter")
- Inappropriate obscure references ("This might remind you of something.")
- Redundancy (mentioning "showing the desktop" when the KCM's header already shows this)

The above issues are fixed.

Test Plan:
Before: {F8129332}
After: {F8129331}

Reviewers: #vdg, #kwin, filipf, zzag

Reviewed By: #vdg, #kwin, filipf, zzag

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D27630

effects/eyeonscreen/package/metadata.desktop

@@ -1,5 +1,5 @@
 [Desktop Entry]
-Name=eye On Screen
+Name=Eye on Screen
 Name[ca]=Ull a la pantalla
 Name[ca@valencia]=Ull en la pantalla
 Name[cs]=oko na obrazovce
@@ -42,7 +42,7 @@ Name[x-test]=xxeye On Screenxx
 Name[zh_CN]=注视屏幕
 Name[zh_TW]=螢幕之眼
 Icon=preferences-system-windows-effect-eyeonscreen
-Comment=Suck windows into desktop to show the latter. This might remind you of something.
+Comment=Suck windows into the desktop
 Comment[ca]=Enganxa les finestres a l'escriptori per a mostrar la darrera. Això podria recordar-vos quelcom.
 Comment[ca@valencia]=Apega les finestres a l'escriptori per a mostrar l'última. Això podria recordar-vos alguna cosa.
 Comment[da]=Sug vinduer ind i skrivebordet for at vise dette. Måske minder det dig om noget.

effects/windowaperture/package/metadata.desktop

@@ -41,7 +41,7 @@ Name[x-test]=xxWindow Aperturexx
 Name[zh_CN]=窗口光圈
 Name[zh_TW]=視窗光圈
 Icon=preferences-system-windows-effect-windowaperture
-Comment=Move window into the corners while showing desktop
+Comment=Move windows into screen corners
 Comment[ca]=Mou la finestra cap a les cantonades en mostrar l'escriptori
 Comment[ca@valencia]=Mou la finestra cap a les cantonades en mostrar l'escriptori
 Comment[da]=Flyt vinduer til hjørnerne når skrivebordet vises