Drop the semantic retriever from libmediapipe.so

MediaPipe 1.1.0 links its SQLite memory and vector stores from prebuilt
archives (third_party/sqlite_prebuilt_files.bzl) built with Google's internal
toolchain: they carry no archive symbol table, reference Google's libc++
(std::__u) and internal symbols (__alloc_token_*__Znwm, sqlite_helpers,
sqlite3_vector_init), and cannot link against a libstdc++ build. Leave the
semantic retriever's C API out of the library; everything else, including
the universal embedder, still builds. Only an explicit import of
mediapipe.tasks.python.retrieval.semantic_retriever needs those symbols.

--- a/mediapipe/tasks/c/BUILD
+++ b/mediapipe/tasks/c/BUILD
@@ -45,7 +45,6 @@
         "//mediapipe/tasks/c/audio/audio_embedder:audio_embedder_c_lib",
         "//mediapipe/tasks/c/core:common",
         "//mediapipe/tasks/c/metadata:flatbuffer_api_c_lib",
-        "//mediapipe/tasks/c/retrieval/semantic_retriever:semantic_retriever_lib",
         "//mediapipe/tasks/c/retrieval/universal_embedder:universal_embedder_lib",
         "//mediapipe/tasks/c/text/language_detector:language_detector_c_lib",
         "//mediapipe/tasks/c/text/text_classifier:text_classifier_c_lib",