Simplify ErrorMarker component

Just support the actual prop in use (`isVisible`) and drop passing a
child.

src/web/components/form/ErrorMarker.jsx

@@ -7,23 +7,26 @@ import React from 'react';
 
 import styled from 'styled-components';
 
-import {styledExcludeProps} from 'web/utils/styledConfig';
 import Theme from 'web/utils/theme';
+import PropTypes from 'web/utils/proptypes';
 
-const StyledMarker = styledExcludeProps(styled.div, ['isVisible'])`
+const StyledMarker = styled.div`
   color: ${Theme.darkRed};
-  color: ${props => props.color};
   font-weight: bold;
   font-size: 19px;
   padding-bottom: 1px;
   padding-left: 4px;
-  display: ${props => (props.isVisible ? 'inline' : 'none')};
+  display: ${props => (props.$isVisible ? 'inline' : 'none')};
 `;
 
-const ErrorMarker = props => (
-  <StyledMarker {...props} data-testid="error-marker">
+const ErrorMarker = ({isVisible}) => (
+  <StyledMarker $isVisible={isVisible} data-testid="error-marker">
     ×
   </StyledMarker>
 );
 
+ErrorMarker.propTypes = {
+  isVisible: PropTypes.bool,
+};
+
 export default ErrorMarker;

src/web/components/form/multiselect.jsx

@@ -277,7 +277,7 @@ class MultiSelect extends React.Component {
                   </Menu>
                 )}
               </SelectContainer>
-              <ErrorMarker isVisible={hasError}>×</ErrorMarker>
+              <ErrorMarker isVisible={hasError} />
             </Div>
           );
         }}

src/web/components/form/select.jsx

@@ -278,7 +278,7 @@ class Select extends React.Component {
                   </Menu>
                 )}
               </SelectContainer>
-              <ErrorMarker isVisible={hasError}>×</ErrorMarker>
+              <ErrorMarker isVisible={hasError} />
             </Div>
           );
         }}

src/web/components/form/textarea.jsx

@@ -79,7 +79,7 @@ const TextArea = ({
         value={value}
         onChange={handleChange}
       />
-      <ErrorMarker isVisible={hasError}>×</ErrorMarker>
+      <ErrorMarker isVisible={hasError} />
     </React.Fragment>
   );
 };

src/web/components/form/textfield.jsx

@@ -19,7 +19,7 @@ const TextField = ({hasError = false, errorContent, title, ...props}) => {
         title={hasError ? `${errorContent}` : title}
         type="text"
       />
-      <ErrorMarker isVisible={hasError}>×</ErrorMarker>
+      <ErrorMarker isVisible={hasError} />
     </React.Fragment>
   );
 };