[flang] Fix build

An unused variable declaration from a recent change is eliciting
a fatal warning; remove it.

GitOrigin-RevId: 5a6c38fbefba981d8e37d78b3d0d7a07d56d1160
diff --git a/lib/Parser/prescan.cpp b/lib/Parser/prescan.cpp
index 1408fdf..0531ffd 100644
--- a/lib/Parser/prescan.cpp
+++ b/lib/Parser/prescan.cpp
@@ -319,7 +319,6 @@
   j += 3;
   static const char *const prefixes[]{"program", "subroutine", "function",
       "blockdata", "module", "submodule", nullptr};
-  CharBlock stmt{tokens.ToCharBlock()};
   bool isPrefix{j == n || !IsLegalInIdentifier(str[j])}; // prefix is END
   std::size_t endOfPrefix{j - 1};
   for (const char *const *p{prefixes}; *p; ++p) {