Clean up several minor issues in setPage

[aarongoldenthal]

The following issues were noticed today in the setPage function (all are low priority cleanup).

• Removed unused url argument from setPage
• Moved debug log entry for navigating to URL to proper location (from setPage to gotoUrl)
• Update debug logging for all setPage operations

Debug log changes:

 > pa11y -d https://pa11y.org

 Welcome to Pa11y

  > Running Pa11y on URL https://pa11y.org
  > Debug: Launching Headless Chrome
- > Debug: Opening URL in Headless Chrome
+ > Debug: Opening new browser page
+ > Debug: Setting page User-Agent to "pa11y/8.0.0"
+ > Debug: Setting page viewport
+ > Debug: Navigating to https://pa11y.org
  > Debug: Loading runner: htmlcs
  > Debug: Injecting Pa11y
  > Debug: Injecting runner: htmlcs
  > Debug: Running Pa11y on the page
  > Debug: Document title: "Pa11y"

 No issues found!