Add sound marker removal regex

[ilkermeliksitki]

Description

Sound file markers are replaced with a space, " ". Consider the following marker.
[sound:......926fd104dec94c802cb89d61d1b8a6f.mp3], which constitutes a lot space in pop up dictionary and does not give any useful information by itself.

Checklist:

Please replace the space inside the brackets with an x and fill out the ellipses if the following items apply:

• I've read and understood the contribution guidelines
• I've tested my changes against at least one of the following Anki builds:
  • Latest standard Anki 2.1 binary build
  • Latest alternative Anki 2.1 binary build
• I've tested my changes on at least one of the following platforms:
  • Linux, version:
  • Windows, version:
  • macOS, version:
• My changes potentially affect non-desktop platforms, of which I've tested:
  • AnkiMobile, version:
  • AnkiDroid, version:
  • AnkiWeb