chore(otel): remove otelbeat (#47804)

The otelbeat binary is not used anymore since we moved to an in-process testing collector in #47338, so remove the subcommand and all references to it in the build system. The otel subcommand was gated behind a build tag and only used in tests.

(cherry picked from commit f4b9ad1)

# Conflicts:
#	x-pack/filebeat/magefile.go
#	x-pack/libbeat/common/otelbeat/otel.go

Author: mauri870

dev-tools/mage/build.go

@@ -198,12 +198,6 @@ func GolangCrossBuild(params BuildArgs) error {
 	return Build(params)
 }
 
-func BuildOTel() error {
-	args := DefaultBuildArgs()
-	args.ExtraFlags = append(args.ExtraFlags, "-tags", "otelbeat")
-	return Build(args)
-}
-
 // Build invokes "go build" to produce a binary.
 func Build(params BuildArgs) error {
 	fmt.Println(">> build: Building", params.Name)

dev-tools/mage/gotest.go

@@ -503,13 +503,6 @@ func BuildSystemTestBinary() error {
 	return BuildSystemTestGoBinary(DefaultTestBinaryArgs())
 }
 
-// BuildSystemTestOTelBinary builds beat binary that includes otel.
-func BuildSystemTestOTelBinary() error {
-	args := DefaultTestBinaryArgs()
-	args.ExtraFlags = []string{"-tags", "otelbeat"}
-	return BuildSystemTestGoBinary(args)
-}
-
 // BuildSystemTestGoBinary build a binary for testing that is instrumented for
 // testing and measuring code coverage. The binary is only instrumented for
 // coverage when TEST_COVERAGE=true (default is false).