remove test_sdists.sh (#9213)

The reason I want to do this is many of the targets of `test_sdists.sh` use Python 3.6 which [has reached its EOL](https://www.python.org/dev/peps/pep-0494/#lifespan). We could instead just stop running the test on these systems or install a newer version of Python 3 outside of OS packaging, but instead I decided to look into why we have these tests to begin with.

I introduced these tests many years ago in https://github.com/certbot/certbot/pull/4089 as a fix for https://github.com/certbot/certbot/issues/4044. Essentially the problem was the way packagers ran tests and the way we ran tests were slightly different. This difference could cause test failures when distros tried to run tests on our packages.

Since I did this, [we've switched to telling packagers to run tests using `pytest` like we do](https://github.com/certbot/certbot/blob/5e76669c5026732d1440e39e93b58220ef7bd354/certbot/docs/packaging.rst#notes-for-package-maintainers) and we've greatly reduced our reliance on OS packaging through things like `snap`.

Because of this, I think we should stop running this test, reducing our reliance on the heavy "test farm tests", and simplifying our CI pipeline. I think future problems here is quite unlikely and even if we have them, it should only affect tests on our non-primary distribution mechanisms which I think is a very minor concern.

When reviewing this PR, it's probably worth noting that I just replaced `targets.yaml` with the contents of `apache2_targets.yaml` since the Apache 2 tests are the only runs we're running with this change.

letstest/targets/targets.yaml

@@ -1,4 +1,7 @@
 # These images are located in us-east-1.
+#
+# All machines must currently use x86_64 since Pebble does not currently
+# publish images for other architectures.
 
 targets:
   #-----------------------------------------------------------------------------
@@ -25,37 +28,12 @@ targets:
     type: ubuntu
     virt: hvm
     user: admin
-  - ami: ami-0dcd54b7d2fff584f
-    name: debian10_arm64
-    type: ubuntu
-    virt: hvm
-    user: admin
-    machine_type: a1.medium
-  #-----------------------------------------------------------------------------
-  # RHEL
-  # These AMIs were found using the commands given at
-  # https://web.archive.org/web/20220129184532/https://access.redhat.com/solutions/15356.
-  - ami: ami-005b7876121b7244d
-    name: RHEL7
-    type: centos
-    virt: hvm
-    user: ec2-user
-  - ami: ami-0c322300a1dd5dc79
-    name: RHEL8
-    type: centos
-    virt: hvm
-    user: ec2-user
   #-----------------------------------------------------------------------------
   # CentOS
-  # These AMIs were found on
+  # This AMI was found on
   # https://web.archive.org/web/20211126215532/https://wiki.centos.org/Cloud/AWS.
   - ami: ami-00e87074e52e6c9f9
     name: centos7
     type: centos
     virt: hvm
     user: centos
-  - ami: ami-0ee70e88eed976a1b
-    name: centos_stream8
-    type: centos
-    virt: hvm
-    user: centos