Add pass that removes spurious panic import function

[athei]

In order to resolve use-ink/ink#364 we should add a pass that removes the imported function and replaces all call sides by an unreachable instruction. This is OK because we assume that the intention of calling this function is to panic anyways.

It might prevent unwinding in cases that is enabled. However, we don't support unwinding anyways so it does not matter.

[cmichi]

As part of this issue the effect of those two PR's should be revoked:
use-ink/ink#1034
#372

[athei]

Replaced by use-ink/ink#1049