[EXPORTER] Prometheus: Remove explicit timestamps from metric points #8518

Job	Run time
CMake gcc 12 (maintainer mode, C++11, async)	12m 52s
CMake gcc 12 (maintainer mode, sync)	15m 38s
CMake test (without otlp-exporter)	7m 10s
CMake test (with abseil)	7m 41s
CMake clang 14 (maintainer mode, sync)	16m 30s
CMake clang 14 (maintainer mode, async)	19m 7s
CMake gcc 4.8 (with otlp exporter)	19m 26s
CMake gcc 4.8 (without otlp exporter)	5m 31s
CMake gcc 12 (maintainer mode, async)	11m 7s
CMake msvc (maintainer mode)	11m 26s
CMake test (with opentracing-shim)	6m 24s
CMake C++20 test(Clang with libc++)	11m 18s
CMake C++20 test(GCC)	14m 35s
CMake test (without otlp-exporter and with async export)	6m 34s
Bazel	19m 30s
Bazel with async export	23m 57s
Bazel with external abseil	20m 6s
CMake do not install test (with otlp-exporter)	25m 26s
CMake install test (with abseil)	6m 19s
CMake test (with modern protobuf,grpc and abseil)	39m 12s
CMake test (build shared libraries with otlp-exporter and static gRPC)	20m 34s
CMake test (with otlp-exporter)	28m 1s
Plugin -> CMake	1m 58s
Bazel asan config	10m 30s
Bazel noexcept	23m 58s
Bazel nortti	18m 56s
Bazel on MacOS	26m 13s
Bazel tsan config	19m 47s
Bazel valgrind	24m 16s
Benchmark	14m 45s
Format	21s
Code coverage	13m 43s
Copyright	8s
DocFX check	1m 3s
misspell	7s
markdown-lint	16s
CMake -> exporter proto	17m 22s
Bazel Windows	39m 36s
Plugin -> CMake Windows	9m 49s
CMake (With async export) -> exporter proto	19m 38s
CMake -> exporter proto (Build as DLL)	17m 29s
	10h 8m 19s

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