[sup-compat] Don't trim trailing whitespace on line introducing quotation.

Ignoring this whitespace seems like a good idea to me, but it's
interfering with my comparisons with sup since sup doesn't do this.

This might be a commit worth dropping in the future since it exists
only for pedantic consistency with sup and not for any reason of its
own.

notmuch-index-message.cc

@@ -377,9 +377,6 @@ gen_terms_body_str (Xapian::TermGenerator term_gen,
 	    continue;
 
 	/* Also skip lines introducing a quote on the next line. */
-	while (line_end > line && isspace (*line_end))
-	    line_end--;
-
 	if (*line_end == ':' && *next_line == '>')
 	    continue;