[diff.dcl] Remove space before colon. (#2599)

Author: Eelis

source/compatibility.tex

@@ -446,7 +446,7 @@
 In the following example, the
 left-hand column presents valid C;
 the right-hand column presents
-equivalent \Cpp{} :
+equivalent \Cpp{}:
 
 \begin{codeblock}
 void f(const parm);            void f(const int parm);