[translation] wording suggestions for settings

For the next translation round it would be nice to have a small cleaning in the source strings, especially in some older subtitles of the settings labels. The latest subtitles are shorter, more precise and don't use a period at the end. That period doesn't look nice and only a few setting points still use it. It's ok for multiple sentences but in these strings the period at the end should be removed to have an equal style (already done here):

1. Disabled: better stability\nDecoding: may improve performance\nFull: may improve performance further
2. Settings when secondary displays are connected (HDMI/Chromecast)
3. Clone the device screen without remote control
4. Change the method that VLC uses to output audio
5. Speed up decoding but could lower video quality
6. Speed up and slow down audio without changing the pitch (requires a fast device)

• suggestions to connect sentences without periods:

1. Changing the deblocking filter settings could improve video quality (advanced users only)
2. RGB 32-bit: default chroma\nRGB 16-bit: better performance but lower quality\nYUV: best performance but does not work on all devices (Android 2.3 and later only)

• Remove all 3 not needed video_group_size-strings from the source translation file

• In this string a different order of the word first would be better for the translation:
  Group by first %s letters