Strip quotes around fileinfo strings

Yosys puts quotes around the string that represents the fileinfo whereas
firrtl does not. So when firrtl sees quotes, it escapes them with an extra
backslash which makes it hard to read afterwards.

backends/firrtl/firrtl.cc

@@ -106,7 +106,11 @@ std::string getFileinfo(dict<RTLIL::IdString, RTLIL::Const> attributes)
 			fileinfo << "]";
 		}
 	}
-	return fileinfo.str();
+
+  std::string fileinfo_str = fileinfo.str();
+  fileinfo_str.erase(std::remove(fileinfo_str.begin(), fileinfo_str.end(), '\"'), fileinfo_str.end());
+
+  return fileinfo_str;
 }
 
 // Get a port direction with respect to a specific module.