Remove unnecessary check and add better textline documentation

common/lib/capa/capa/inputtypes.py

@@ -457,8 +457,16 @@ class TextLine(InputTypeBase):
     """
     A text line input.  Can do math preview if "math"="1" is specified.
 
+    If "trailing_text" is set to a value, then the textline will be shown with the value after the text input. 
+    This is useful if you would like to specify a specific type of units for the text input.
+
     If the hidden attribute is specified, the textline is hidden and the input id is stored in a div with name equal
     to the value of the hidden attribute.  This is used e.g. for embedding simulations turned into questions.
+
+    Example:
+        <texline math="1" trailing_text="m/s" />
+
+    This example will render out a text line with a math preview and the text 'm/s' after the end of the text line.
     """
 
     template = "textline.html"

common/lib/capa/capa/templates/textline.html

@@ -31,9 +31,7 @@
             style="display:none;"
         % endif
    />
-   % if trailing_text:
    ${trailing_text}
-   % endif
 
       <p class="status">
         % if status == 'unsubmitted':