Customize function to provide a minimal configuration for profiling

Can be included with the following snippet in the configuration:

    from RecoPixelVertexing.Configuration.customizePixelTracksForProfiling import customizePixelTracksForProfiling
    process = customizePixelTracksForProfiling(process)

Removes validation, DQM, and output modules.
As suggested in cms-patatrack#70 (comment), an `AsciiOutputModule` is used to require the `pixelTracks`.

Backport from the Patatrack fork (cms-patatrack#106).

RecoPixelVertexing/Configuration/python/customizePixelTracksForProfiling.py

@@ -0,0 +1,15 @@
+import FWCore.ParameterSet.Config as cms
+
+def customizePixelTracksForProfiling(process):
+    process.out = cms.OutputModule("AsciiOutputModule",
+        outputCommands = cms.untracked.vstring(
+            "keep *_pixelTracks_*_*",
+        ),
+        verbosity = cms.untracked.uint32(0),
+    )
+
+    process.outPath = cms.EndPath(process.out)
+
+    process.schedule = cms.Schedule(process.raw2digi_step, process.reconstruction_step, process.outPath)
+
+    return process