Do not load amssymb if not needed (#6762)

Fixes #6469. From https://tex.stackexchange.com/a/549938

data/templates/default.latex

@@ -97,15 +97,17 @@ $endif$
 $if(linestretch)$
 \usepackage{setspace}
 $endif$
-\usepackage{amssymb,amsmath}
+\usepackage{amsmath}
 \usepackage{ifxetex,ifluatex}
 \ifnum 0\ifxetex 1\fi\ifluatex 1\fi=0 % if pdftex
   \usepackage[$if(fontenc)$$fontenc$$else$T1$endif$]{fontenc}
   \usepackage[utf8]{inputenc}
   \usepackage{textcomp} % provide euro and other symbols
+  \usepackage{amssymb}
 \else % if luatex or xetex
 $if(mathspec)$
   \ifxetex
+    \usepackage{amssymb}
     \usepackage{mathspec}
   \else
     \usepackage{unicode-math}