Remove the GraalVM workarounds that are no longer required with 19.3.1

[gwenneg]

As suggested by @jaikiran here, we introduced several workarounds for GraalVM issues into the Quarkus code lately. Most of them were introduced to fix GraalVM 19.3.0 issues but we also did that for previous GraalVM versions. Once GraalVM 19.3.1 is there, we should remove from the Quarkus code all of these workarounds that are no longer required because they were fixed in GraalVM itself.

Let's start a list of the workarounds that should be removed:

• Substitute BootLoader.hasClassPath() to work around a JDK 11 NPE #6090 Removed in Update GraalVM to 19.3.0.2 #6364
• Substitute BootLoader.loadClassOrNull(name) to fix a NPE with JDK 11 #6169 Removed in Update GraalVM to 19.3.0.2 #6364
• io.quarkus.runtime.graal.FieldReplacement Removed in Drop GraalVM 19.2.1 support and deprecate enableJni option #6792
• io.quarkus.vertx.core.runtime.graal.Target_sun_nio_ch_DatagramChannelImpl Removed in Remove unused Vert.x GraalVM substitution #6449
• 43e36e5
• 0f2d90f Removed in Update GraalVM to 19.3.0.2 #6364
• 85d8746 Tests done with GraalVM 19.3.1 showed that this commit shouldn't be removed

[gsmet]

@gwenneg what's the status of this one?

[gwenneg]

I didn't try to remove 43e36e5 so far and I'm not sure 85d8746 actually needs to be removed. I'll take a look at it tonight.