prometheusreceiver: remove unused buffer_period and buffer_count configuration options (#24257)

**Description:**

Fixes #24258

Found while adding documentation for
#24256.
The prometheus receiver had two config options that AFAICT have never
been used.

The config options have existed since the very first commit ever for the
Prometheus receiver:
7c728ef


Co-authored-by: Dmitrii Anoshin <[email protected]>

Author: dashpole

.chloggen/prometheus-config-cleanup.yaml

@@ -0,0 +1,20 @@
+# Use this changelog template to create an entry for release notes.
+# If your change doesn't affect end users, such as a test fix or a tooling change,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: 'breaking'
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: prometheusreciever
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Remove unused buffer_period and buffer_count configuration options
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [24258]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

receiver/prometheusreceiver/config.go

@@ -34,8 +34,6 @@ const (
 type Config struct {
 	PrometheusConfig   *promconfig.Config `mapstructure:"-"`
 	TrimMetricSuffixes bool               `mapstructure:"trim_metric_suffixes"`
-	BufferPeriod       time.Duration      `mapstructure:"buffer_period"`
-	BufferCount        int                `mapstructure:"buffer_count"`
 	// UseStartTimeMetric enables retrieving the start time of all counter metrics
 	// from the process_start_time_seconds metric. This is only correct if all counters on that endpoint
 	// started after the process start time, and the process is the only actor exporting the metric after

receiver/prometheusreceiver/testdata/config.yaml

@@ -1,7 +1,5 @@
 prometheus:
 prometheus/customname:
-  buffer_period: 234
-  buffer_count: 45
   trim_metric_suffixes: true
   use_start_time_metric: true
   start_time_metric_regex: '^(.+_)*process_start_time_seconds$'

receiver/prometheusreceiver/testdata/invalid-config-prometheus-unsupported-features.yaml

@@ -1,6 +1,4 @@
 prometheus:
-  buffer_period: 234
-  buffer_count: 45
   use_start_time_metric: true
   start_time_metric_regex: '^(.+_)*process_start_time_seconds$'
   config: