Theorem style: set NextNoIndent to 0

Theorem style: set NextNoIndent to 0

After a Theorem environment, LaTeX does by default indent the
following paragraph.

I checked various classes and no ModifyStyle was needed. The
hollywood and broadway classes are strange cases where there is an
indent after the Theorem environment, but it is much smaller than
the normal indent. The indent is the same as the opening indent of
normal text, which we currently ignore. Further, I don't expect it
is common to use theorems in these classes.