kv-cache : remove LLAMA_SET_ROWS checks (#15505)

ggml-ci

src/llama-context.h

@@ -283,10 +283,6 @@ private:
 
     bool has_evaluated_once = false;
 
-    // env: LLAMA_SET_ROWS (temporary)
-    // ref: https://github.com/ggml-org/llama.cpp/pull/14285
-    bool supports_set_rows = true;
-
     // env: LLAMA_GRAPH_REUSE_DISABLE
     bool graph_reuse_disable = false;