[UR] Fix UR_ENABLE_LAYERS parsing

During context creation UR_ENABLE_LAYERS was being incorrectly parsed
expecting key-value pairs, but its supposed to accept a comma separated
list of arguments.

Author: kswiecicki

unified-runtime/source/loader/ur_lib.cpp

@@ -38,14 +38,14 @@ context_t::context_t() { parseEnvEnabledLayers(); }
 context_t::~context_t() {}
 
 void context_t::parseEnvEnabledLayers() {
-  auto maybeEnableEnvVarMap = getenv_to_map("UR_ENABLE_LAYERS", false);
-  if (!maybeEnableEnvVarMap.has_value()) {
+  auto maybeEnableEnvVarVec = getenv_to_vec("UR_ENABLE_LAYERS");
+  if (!maybeEnableEnvVarVec.has_value()) {
     return;
   }
-  auto enableEnvVarMap = maybeEnableEnvVarMap.value();
+  auto enableEnvVarVec = maybeEnableEnvVarVec.value();
 
-  for (auto &key : enableEnvVarMap) {
-    enabledLayerNames.insert(key.first);
+  for (auto &layer : enableEnvVarVec) {
+    enabledLayerNames.insert(layer);
   }
 }