Clean up single namespace forward-declarations

Done using the following ruby script:

Dir.glob('**/*.h').each { |file|
  if File.file?(file)
    s = File.read(file)
    t = s.gsub(/^namespace .+ \{\n\s*class .*;\n\s*\}.*$/) { |m| m.gsub(/\n\s*/, ' ').gsub(/\s*\/\/.*$/, '') }
    if t != s
      puts file
      File.open(file, 'w').write(t)
    end
  end
}

Change-Id: Iffcb966e90eb8e1a625eccd5dd0b94f000ae368e
Reviewed-by: hjk <hjk121@nokiamail.com>