fix: workaround for otel agent dependency causes orchestrion failure

Moved the blank import of `go.opentelemetry.io/collector/pdata/pprofile``
which was introduced to avoid `go mod tidy` from failing to resolve a
coherent dependency closure into a new file guarded by a build tag so
that it is not present in builds uder normal circumstances.

This removes a dependency cycle caused by the `pprofile` package having
a transitive dependency on `net/http`, while the
`gopkg.in/DataDog/dd-trace-go.v1/internal` package is imported some code
that is injected by orchestrion into `net/http` itself (resulting in a
cycle, breaking builds).

internal/agent.go

@@ -11,14 +11,6 @@ import (
 	"os"
 
 	"gopkg.in/DataDog/dd-trace-go.v1/internal/log"
-
-	// OTel did a breaking change to the module go.opentelemetry.io/collector/pdata which is imported by the agent
-	// and go.opentelemetry.io/collector/pdata/pprofile depends on it and is breaking because of it
-	// For some reason the dependency closure won't let use upgrade this module past the point where it does not break anymore
-	// So we are forced to add a blank import of this module to give us back the control over its version
-	//
-	// TODO: remove this once github.com/datadog-agent/pkg/trace has upgraded both modules past the breaking change
-	_ "go.opentelemetry.io/collector/pdata/pprofile"
 )
 
 const (