[clang] remove accidental full stop at the end of the sentence

Author: Tsche

clang/docs/UsersManual.rst

@@ -4028,7 +4028,7 @@ Controlling implementation limits
   Sets the limit for the number of full-expressions evaluated in a single
   constant expression evaluation. This also controls the maximum size
   of array and dynamic array allocation that can be constant evaluated.
-  The default is 1048576, and the limit can be disabled with `-fconstexpr-steps=0`..
+  The default is 1048576, and the limit can be disabled with `-fconstexpr-steps=0`.
 
 .. option:: -ftemplate-depth=N