configure: fix --help alignment

configure: fix --help alignment

AC_ARG_ENABLE seems to only trim off whitespace from the start and end
of its help-string argument, while prepending two spaces of indentation
to all lines.

This means that the two spaces of indentation between the --enable-rtsp
and the --disable-rtsp line were not removed causing ./configure --help
to print:

  Optional Features:
    [...]
    --enable-rtsp           Enable RTSP support
      --disable-rtsp          Disable RTSP support

I removed the indentation to fix the issue, now it prints:

  Optional Features:
    [...]
    --enable-rtsp           Enable RTSP support
    --disable-rtsp          Disable RTSP support

The --enable-hsts and --disable-hsts lines had the same problems, and
have been fixed too.

Closes #11142