Fix #9501: htmlreport: Line number position is shifted (#2480)

The 1 pixel dotted border that is drawn around every Cppcheck error
message adds 2 extra pixels for every line with an error message.
For more than very few error messages in a file the discrepancy is
clearly visible and line numbering gets wrong.
This commit removes the dotted border as it is not necessary.
The error message is highlighted with a red background and is still
clearly visible.

htmlreport/cppcheck-htmlreport

@@ -43,7 +43,6 @@ h1 {
 
 .error2 {
     background-color: #faa;
-    border: 1px dotted black;
     display: inline-block;
     margin-left: 4px;
 }