Remove the obsolete --enable-heapdump command line arg

[mykola-mokhnach]

Proposed changes

Node12 introduced the built-in heap dumping feature, so it is time to get rid of the custom heapdump module usage (especially taking into account it's native and does not always compile properly for newer Node releases)

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

[coveralls]

Coverage remained the same at 90.211% when pulling a25f2f1 on mykola-mokhnach:rm_heapdump into 3d7a011 on appium:master.