Avoid failed compilations caused by JDK classes without zero argument constructors

[kelloggm]

E.g., in https://github.com/plume-lib/plume-util/blob/master/src/main/java/org/plumelib/util/EntryReader.java, if all the constructors are removed, we get compilation errors of the following form:

public class EntryReader extends LineNumberReader implements Iterator<String> {
       ^
    constructor LineNumberReader.LineNumberReader(Reader) is not applicable
      (actual and formal argument lists differ in length)
    constructor LineNumberReader.LineNumberReader(Reader,int) is not applicable
      (actual and formal argument lists differ in length)
1 error

I don't actually expect this PR to move the needle on plume-util compilation numbers, because fixing this problem exposed another issue in compiling the EntryReader class mentioned above (Specimin is incorrectly assuming that private classes can be referenced outside their containing class). That's a separate issue that I'll address in a new PR.

[kelloggm]

I've just realized that I made an error here. This PR is not yet ready to go - the script I was using to test it was checking the wrong target method (which is why I was seeing that other error). Still, the issue is probably fixable, but I'll come back to it later.

[kelloggm]

@M3CHR0M4NC3R this is now ready for review

[kelloggm]

CI is failing, so this is not ready for review.