VM should remove abstract modifier for methods

[gbracha]

See issue #3898

[iposva-google]

Removed this from the M1 milestone.
Added this to the M2 milestone.

[iposva-google]

Removed this from the M2 milestone.
Added this to the M3 milestone.

[DartBot]

This comment was originally written by @mhausner

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Fixed at revision 17243.

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Set owner to @mhausner.
Added Fixed label.