[EXPORTER] Prometheus: Remove explicit timestamps from metric points #8519

Job	Run time
CMake clang 14 (maintainer mode, async)	17m 31s
CMake test (with abseil)	9m 45s
CMake clang 14 (maintainer mode, sync)	17m 20s
CMake gcc 4.8 (with otlp exporter)	17m 25s
CMake gcc 4.8 (without otlp exporter)	5m 57s
CMake gcc 12 (maintainer mode, async)	12m 29s
CMake gcc 12 (maintainer mode, C++11, async)	11m 38s
CMake gcc 12 (maintainer mode, sync)	10m 46s
CMake msvc (maintainer mode)	11m 39s
CMake test (with opentracing-shim)	6m 11s
CMake test (with otlp-exporter)	21m 13s
CMake test (without otlp-exporter)	6m 38s
CMake C++20 test(Clang with libc++)	11m 58s
CMake C++20 test(GCC)	12m 5s
CMake test (without otlp-exporter and with async export)	8m 10s
Bazel noexcept	19m 3s
Bazel	27m 10s
Bazel nortti	19m 56s
Bazel with async export	18m 54s
Bazel valgrind	31m 21s
Bazel with external abseil	18m 51s
CMake do not install test (with otlp-exporter)	29m 45s
CMake install test (with abseil)	6m 21s
CMake test (with modern protobuf,grpc and abseil)	29m 36s
CMake test (build shared libraries with otlp-exporter and static gRPC)	21m 20s
Plugin -> CMake	1m 38s
Bazel asan config	10m 23s
Bazel on MacOS	27m 2s
Bazel tsan config	20m 37s
Benchmark	12m 19s
Code coverage	16m 27s
Copyright	7s
DocFX check	59s
Format	25s
markdown-lint	9s
misspell	5s
CMake -> exporter proto	17m 26s
Bazel Windows	35m 32s
Plugin -> CMake Windows	9m 14s
CMake (With async export) -> exporter proto	16m 51s
CMake -> exporter proto (Build as DLL)	16m 54s
	9h 49m 10s

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