context CHANGE simplify use of ly_ctx_unset_searchpaths()

Accept searchdir string instead of the index.
diff --git a/src/context.c b/src/context.c
index 386ee05..d790c87 100644
--- a/src/context.c
+++ b/src/context.c
@@ -125,18 +125,29 @@
 }
 
 API LY_ERR
-ly_ctx_unset_searchdirs(struct ly_ctx *ctx, int index)
+ly_ctx_unset_searchdirs(struct ly_ctx *ctx, const char *value)
 {
+    unsigned int index;
+
     LY_CHECK_ARG_RET(ctx, ctx, LY_EINVAL);
-    LY_CHECK_ERR_RET(index >= 0 && (unsigned int)index >= ctx->search_paths.count, LOGARG(ctx, index), LY_EINVAL);
 
     if (!ctx->search_paths.count) {
         return LY_SUCCESS;
     }
 
-    if (index >= 0) {
+    if (value) {
         /* remove specific search directory */
-        return ly_set_rm_index(&ctx->search_paths, index, free);
+        for (index = 0; index < ctx->search_paths.count; ++index) {
+            if (!strcmp(value, ctx->search_paths.objs[index])) {
+                break;
+            }
+        }
+        if (index == ctx->search_paths.count) {
+            LOGARG(ctx, value);
+            return LY_EINVAL;
+        } else {
+            return ly_set_rm_index(&ctx->search_paths, index, free);
+        }
     } else {
         /* remove them all */
         ly_set_erase(&ctx->search_paths, free);
diff --git a/src/libyang.h b/src/libyang.h
index 1a117af..9b850e1 100644
--- a/src/libyang.h
+++ b/src/libyang.h
@@ -115,11 +115,10 @@
  * @brief Clean the search path(s) from the libyang context
  *
  * @param[in] ctx Context to be modified.
- * @param[in] index Index of the search path to be removed, use negative value to remove them all.
- *            Correct index value can be checked via ly_ctx_get_searchdirs().
+ * @param[in] value Searchdir to be removed, use NULL to remove them all.
  * @return LY_ERR return value
  */
-LY_ERR ly_ctx_unset_searchdirs(struct ly_ctx *ctx, int index);
+LY_ERR ly_ctx_unset_searchdirs(struct ly_ctx *ctx, const char *value);
 
 /**
  * @brief Get the NULL-terminated list of the search paths in libyang context. Do not modify the result!