build: Remove usage of obsolescent egrep

* "egrep: warning: egrep is obsolescent; using grep -E"
* egrep on haiku is a shell script calling grep -E
* given the warnings in the latest egrep, lets get

build: Remove usage of obsolescent egrep

* "egrep: warning: egrep is obsolescent; using grep -E"
* egrep on haiku is a shell script calling grep -E
* given the warnings in the latest egrep, lets get
ahead of the curve and migrate to grep -E

Change-Id: I0fc2b936c7a9c52f87caf97d8e9ac42516fee014
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5718
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

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