Remove redundant lowercase check.

Change-Id: I332ba23b4f9d4f65de0d27dd4ce906363d01049b
Reviewed-on: https://code-review.googlesource.com/12431
Reviewed-by: Paul Wankadia <junyer@google.com>

re2/tostring.cc

diff --git a/re2/tostring.cc b/re2/tostring.cc
index fc9faca..278c310 100644
--- a/re2/tostring.cc
+++ b/re2/tostring.cc
@@ -131,8 +131,7 @@
     t->append(1, '\\');
     t->append(1, static_cast<char>(r));
   } else if (foldcase && 'a' <= r && r <= 'z') {
-    if ('a' <= r && r <= 'z')
-      r += 'A' - 'a';
+    r -= 'a' - 'A';
     t->append(1, '[');
     t->append(1, static_cast<char>(r));
     t->append(1, static_cast<char>(r) + 'a' - 'A');