[FLINK-9803] Drop canEqual() from TypeSerializer

[aljoscha]

What is the purpose of the change

This change removes TypeSerializer.canEqual() because it is not useful on that class hierachy. Serializers can only equals() on an exact match, not with different serializers up and down the hierarchy.

Verifying this change

This is covered by existing tests. We simply remove the method in the interface and all subclasses.

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  • Needs attention by @igalshilman, @tzulitai [PMC]
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[aljoscha]

@flinkbot attention @tzulitai @igalshilman

[igalshilman]

All and all, 👍 for removing dead code.

There might be a slight potential issue with InstantSerializer since it does not define a serialVersionUID and removing the canEqual will change the auto generated value.

Can you please add to InstantSeiralizer:
private static final long serialVersionUID = -4131715684999061277L;

Guess we'll have to wait for Travis, but other than that LGTM.

[tzulitai]

LGTM 👍

[aljoscha]

Merged. Thanks for the reviews!