Overloaded removeHighlights method to allow us to remove lineNumbers by fileName or all highlights by a username.

extension.ts and highlighter.ts

--- extension.ts :: line 482 ---

function removeHighlight(username: string): void;
function removeHighlight(lineNumber: number, fileName: string, deferRefresh?: boolean): void;
function removeHighlight(
  searchQuery: string | number,
  fileName?: string,
  deferRefresh?: boolean
) {

  // If the searchQuery is a string (username)
  if (isNaN(Number(searchQuery))) {
    const username = searchQuery as string;
    highlighters.forEach(highlighter => highlighter.removeDecorations(username));
  }
  // the searchQuery is a number (lineNumber)
  else {
    if (!fileName) { return; } // the fileName should always be truthy, but tslint generates warnings.

    const existingHighlight = findHighlighter(fileName);
    if (!existingHighlight) {
      console.warn(`Highlight not found so can't unhighlight the line from file`);
      return;
    }

    const lineNumber = searchQuery as number;
    existingHighlight.removeDecoration(lineNumber);
  }

  if (!deferRefresh) {
    triggerUpdateDecorations();
    twitchHighlighterTreeView.refresh();
  }

}

--- highlighter.ts :: line 32 ---

removeDecorations(username: string): Highlight[] {
  this.highlights = this.highlights.filter(highlight => highlight.twitchUser !== username);
  return this.highlights;
}