asn1_SUITE: Remove useless test_driver_load/1 test case

The PER back-end no longer use a driver (or even a NIF),
and the test case would not fail if it didn't work because the
spawned processed were not linked.
asn1_SUITE: Remove unused function case_dir/2
asn_SUITE: Fold per_GeneralString/1 into h323test

The per_GeneralString/1 test case compiles MULTIMEDIA-SYSTEM-CONTROL
and then does a single decoding. Save some compilation time by folding
the test into the h323test/1 test case.
asn1_SUITE: Remove useless test case testInvokeMod/1

It seems that the original purpose is to test encoding by
directly calling the module (as opposed to calling indirectly
using asn1rt). That is tested in many other test cases (such
as testPrimStrings); thus this test case no longer serves any
useful purpose.
asn1ct_parser2: Clean the process dictionary after parsing

Apart from cleanliness, the test suite runs many tests cases in
parallel, so it never hurts to reduce the memory pressure.
asn1ct_gen: Clean up process dictionary after generating

Cleanliness.
asn1_SUITE: Combine most tests that use External.asn1

By combining most tests that use External.asn,
we will only need to compile that spec once instead of 11 times.

While combining the test cases, make sure to remove the redundant code
in testPrimExternal/1 that tests primitive strings in exactly the same
way as testPrimString/1. Removing the redundant code shaves off a few
seconds of testing time.

Keep testSeqExtension/1 as a separate test case, since it is a
complicated test case that does hairy stuff to the source files.
Slightly clean up testX420
asn1_test_lib: Remove unnecessary loading of a compiled ASN.1 spec

asn1ct:compile/2 calls c:c/2 to invoke the compiler and to load
the compiled code. That means that there is no need load the module
after having invoked the ASN.1 compiler.

To make sure that we'll notice if that behavior changes in the future,
extend the rtUI/1 test case to verify that the loaded module has
the correct encoding rule (if asn1ct:compile/2 would fail to reload
the module, the previous encoding rule would be returned).

While at it, it also makes sense to test calling M:bit_string_format/0
to ensure that it continues working.
Remove unused compile() functions
ASN.1 tests: Remove unused choice_extension.erl

The testChoExtension module tests the same thing (and more) as
choice_extension.erl.
asn1_SUITE: Reinstate test of sub-constraint

A test of sub-constraints for PER/UPER was lost in commit 9ec0a0babace.
Remove unused pem_performance.erl file

The module tests the performance of the OTP-PUB-KEY module in the
public_key application, so it is off-topic and should not be
reinstated.
ASN.1 tests: Don't export functions that are only locally called
testMegaco: Remove unused exported function msg11/0

Also remove records, defines, and request/4 that were only used
by msg11/0.
Move out specific tests from asn1_test_lib

asn1_test_lib is supposed to be a general-purpose helper module for
test cases. Move all specific test cases into asn1_SUITE.
Don't allow unused exported functions in test case helpers

To keep the test case clean, add an xref test case to ensure that
there are no unused functions in the any of the test case helper
modules. Eliminate 4 functions that were exported just so that
timer:tc/3 could be used (use timer:tc/1 with a fun instead).
Makefile: Release Emakefile to ensure warnings are treated as errors

The generated Emakefile was not copied when releasing the test
suites, which meant that the suites were compiled with default
options (without the 'warnings_as_errors' option in the generated
Emakefile).

While at it, eliminate left-over dependecies.
asn1_test_lib: Add roundtrip functions and use them everywhere

Even if the roundtrip functions are very simply, putting them here
makes it possible to change its behavior in one place (e.g. if we
are to change encode and decode not to wrap the result in a ok tuple
in some future release).
Simplify tests of CHOICE with OPTIONAL

Test ChoOptional and ChoOptionalImplicitTag with the same test code
and data.