LaTeX: fix a ad3235421 regression with pre_box-shadow-TeXcolor

The internally used color name for the (optional) shadow of
code-blocks had changed at one place but not another, so
using pre_box-shadow-TeXcolor option of 'sphinxsetup'
with latex_elements was broken since.

sphinx/texinputs/sphinx.sty

@@ -595,6 +595,7 @@ will be set to white}%
 }
 %          macro prefix    option prefix    color name prefix
 \spx@tempa{spx@pre@}      {pre_}            {Verbatim}
+    % (memo: internal VerbatimShadowColor was formerly sphinxVerbatimShadowColor)
     % internal legacy color name is VerbatimColor not VerbatimBgColor, so redefine:
     \define@key{sphinx}{pre_background-TeXcolor}%
       {\spx@pre@withbackgroundcolortrue\spx@defineorletcolor{VerbatimColor}#1\relax}%

sphinx/texinputs/sphinxlatexliterals.sty

@@ -210,7 +210,7 @@
 \def\spx@verb@boxes@fcolorbox@setup{%
     % Prepares usage of \spx@boxes@fcolorbox
     \spx@boxes@fcolorbox@setup
-        {pre}{VerbatimBorderColor}{VerbatimColor}{sphinxVerbatimShadowColor}%
+        {pre}{VerbatimBorderColor}{VerbatimColor}{VerbatimShadowColor}%
     \ifspx@opt@verbatimwithframe
     \else
        \spx@boxes@border@top\z@

sphinx/texinputs/sphinxpackageboxes.sty

@@ -76,8 +76,8 @@
 \newdimen\spx@boxes@radius@bottomright
 \newdimen\spx@boxes@radius@bottomleft
 %
-% These colours have to be defined appropriately by the callers, if the
-% corresponding booleans are set to true
+% These colors will be set to colors defined appropriately by caller of
+% \spx@boxes@fcolorbox@setup macro
 % spx@boxes@bordercolor
 % spx@boxes@backgroundcolor
 % spx@boxes@shadowcolor