util: remove unnecessary trim/trimLeft/trimRight wrappers

When needed, use boost::algorithm::trim/trim_left/trim_right directly.

Change-Id: I854d89e553c70ab20679a38922cec306fc57824d
Refs: #3006
diff --git a/src/util/string-helper.hpp b/src/util/string-helper.hpp
index 7785f69..3f1a303 100644
--- a/src/util/string-helper.hpp
+++ b/src/util/string-helper.hpp
@@ -23,10 +23,11 @@
 #define NDN_UTIL_STRING_HELPER_HPP
 
 #include "../common.hpp"
-#include "../encoding/buffer.hpp"
 
 namespace ndn {
 
+class Buffer;
+
 class StringHelperError : public std::invalid_argument
 {
 public:
@@ -111,24 +112,6 @@
 fromHex(const std::string& hexString);
 
 /**
- * @brief Modify str in place to erase whitespace on the left
- */
-void
-trimLeft(std::string& str);
-
-/**
- * @brief Modify str in place to erase whitespace on the right
- */
-void
-trimRight(std::string& str);
-
-/**
- * @brief Modify str in place to erase whitespace on the left and right
- */
-void
-trim(std::string& str);
-
-/**
  * @brief Decode a percent-encoded string
  * @see RFC 3986 section 2
  *