remove a bunch of <functional> includes

This forces us to use an explicit hash class in a few place, but it
is cleaner.

remove utils::lower_bound and utils::upper_bound, which were not used.

libs/utils/test/test_CString.cpp

@@ -36,7 +36,7 @@ TEST(StaticString, hash) {
     EXPECT_NE(a.getHash(), c.getHash());
     EXPECT_NE(b.getHash(), c.getHash());
 
-    std::hash<StaticString> ha;
+    StaticString::Hasher ha;
     EXPECT_EQ(ha(a), a.getHash());
 }