[exporters/prometheus] Get rid of friend test (#2329) #8531

Job	Run time
Bazel on MacOS	29m 32s
Bazel noexcept	18m 26s
Bazel nortti	18m 49s
Bazel asan config	10m 33s
Bazel	20m 9s
Bazel with async export	20m 0s
Bazel tsan config	24m 44s
Bazel valgrind	23m 31s
Bazel with external abseil	24m 55s
Benchmark	12m 31s
CMake test (with abseil)	6m 38s
CMake clang 14 (maintainer mode, async)	17m 58s
CMake clang 14 (maintainer mode, sync)	17m 21s
CMake do not install test (with otlp-exporter)	24m 28s
CMake gcc 4.8 (with otlp exporter)	14m 27s
CMake gcc 4.8 (without otlp exporter)	5m 46s
CMake gcc 12 (maintainer mode, async)	11m 18s
CMake gcc 12 (maintainer mode, C++11, async)	12m 52s
CMake gcc 12 (maintainer mode, sync)	10m 47s
CMake install test (with abseil)	6m 28s
CMake test (with modern protobuf,grpc and abseil)	39m 36s
CMake msvc (maintainer mode)	15m 20s
CMake test (build shared libraries with otlp-exporter and static gRPC)	20m 5s
CMake test (with opentracing-shim)	6m 22s
CMake test (with otlp-exporter)	20m 52s
CMake test (without otlp-exporter)	9m 32s
CMake C++20 test(Clang with libc++)	11m 37s
CMake C++20 test(GCC)	12m 16s
CMake test (without otlp-exporter and with async export)	9m 35s
Code coverage	13m 57s
Copyright	7s
DocFX check	1m 20s
Format	23s
markdown-lint	10s
misspell	4s
Plugin -> CMake	1m 38s
CMake -> exporter proto	23m 33s
Bazel Windows	47m 36s
Plugin -> CMake Windows	10m 20s
CMake (With async export) -> exporter proto	18m 21s
CMake -> exporter proto (Build as DLL)	18m 34s
	10h 12m 31s

Provide feedback