[exporters/prometheus] Omit underscore suffix for unitless metrics #8511

Job	Run time
Bazel asan config	12m 45s
Bazel noexcept	28m 9s
Bazel nortti	27m 54s
Bazel on MacOS	26m 9s
Bazel	20m 29s
Bazel with async export	20m 25s
Bazel tsan config	19m 34s
Bazel valgrind	27m 40s
Bazel with external abseil	28m 38s
Benchmark	12m 35s
CMake test (with abseil)	6m 9s
CMake clang 14 (maintainer mode, async)	17m 32s
CMake clang 14 (maintainer mode, sync)	19m 49s
CMake do not install test (with otlp-exporter)	21m 7s
CMake gcc 4.8 (with otlp exporter)	13m 36s
CMake gcc 12 (maintainer mode, async)	10m 35s
CMake gcc 4.8 (without otlp exporter)	7m 18s
CMake gcc 12 (maintainer mode, C++11, async)	10m 22s
CMake gcc 12 (maintainer mode, sync)	13m 19s
CMake install test (with abseil)	6m 45s
CMake test (with modern protobuf,grpc and abseil)	29m 41s
CMake test (with opentracing-shim)	7m 44s
CMake msvc (maintainer mode)	10m 36s
CMake test (build shared libraries with otlp-exporter and static gRPC)	23m 0s
CMake test (with otlp-exporter)	25m 27s
CMake test (without otlp-exporter)	6m 23s
CMake C++20 test(Clang with libc++)	11m 4s
CMake C++20 test(GCC)	11m 34s
CMake test (without otlp-exporter and with async export)	6m 37s
Code coverage	14m 15s
Copyright	9s
DocFX check	1m 42s
Format	17s
markdown-lint	10s
misspell	7s
Plugin -> CMake	1m 25s
CMake -> exporter proto	17m 45s
Bazel Windows	35m 25s
Plugin -> CMake Windows	9m 44s
CMake (With async export) -> exporter proto	20m 34s
CMake -> exporter proto (Build as DLL)	17m 59s
	10h 2m 28s

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