Do not explicitely define Exec lines for KCMs

See frameworks/kservice!16
CCBUG: 398803

kcms/colors/kcm_colors.desktop

 [Desktop Entry]
-Exec=kcmshell5 kcm_colors
 Icon=preferences-desktop-color
 Type=Service
 X-KDE-ServiceTypes=KCModule

kcms/cursortheme/kcm_cursortheme.desktop

 [Desktop Entry]
-Exec=kcmshell5 kcm_cursortheme
 Icon=preferences-desktop-cursors
 Type=Service
 

kcms/desktoptheme/kcm_desktoptheme.desktop

 [Desktop Entry]
 Icon=preferences-desktop-plasma-theme
-Exec=kcmshell5 kcm_desktoptheme
 
 Type=Service
 X-KDE-ServiceTypes=KCModule

kcms/feedback/kcm_feedback.desktop

 [Desktop Entry]
-Exec=kcmshell5 feedback
 Icon=preferences-desktop-locale
 Type=Service
 X-KDE-ServiceTypes=KCModule

kcms/fonts/kcm_fonts.desktop

 [Desktop Entry]
-Exec=kcmshell5 fonts
 Icon=preferences-desktop-font
 Type=Service
 X-KDE-ServiceTypes=KCModule

kcms/icons/kcm_icons.desktop

 [Desktop Entry]
-Exec=kcmshell5 icons
 Icon=preferences-desktop-icons
 Type=Service
 X-KDE-ServiceTypes=KCModule

kcms/kfontinst/kcmfontinst/fontinst.desktop

 [Desktop Entry]
-Exec=kcmshell5 fontinst
 Icon=preferences-desktop-font-installer
 Type=Service
 X-KDE-ServiceTypes=KCModule

kcms/lookandfeel/kcm_lookandfeel.desktop

 [Desktop Entry]
 Icon=preferences-desktop-theme-global
-Exec=kcmshell5 kcm_lookandfeel
 
 Type=Service
 X-KDE-ServiceTypes=KCModule

kcms/style/kcm_style.desktop

 [Desktop Entry]
-Exec=kcmshell5 style
 Icon=preferences-desktop-theme-applications
 Type=Service
 X-KDE-ServiceTypes=KCModule,KCModuleInit

kcms/translations/kcm_translations.desktop

 [Desktop Entry]
-Exec=kcmshell5 translations
 Icon=preferences-desktop-locale
 Type=Service
 X-KDE-ServiceTypes=KCModule