t/t-clone.sh: remove test skip checks for libnss3

In commit e4e5ada of PR git-lfs#5882 we
added an initial check to the t/t-clone.sh test script which detects
whether libcurl is linked against the legacy libnss3 library on Linux,
and if so, sets a GIT_LIBNSS variable.  We then check that variable
at the start of several tests in the script, and if it is set, skip
performing the tests.

This workaround was introduced because the libnss3 library rejects
TLS/SSL certificates which have both an Extended Key Usage attribute
for TLS Web Server Authentication and a Basic Constraint setting of
"CA:TRUE", and the self-signed certificate used by our lfstest-gitserver
utility program has both attributes, so our tests would otherwise fail.

The only platform on which our tests run which used the legacy libnss3
library was the one based on Red Hat Enterprise Linux (RHEL) 7.  All
the distribution versions based on RHEL 7, CentOS 7, and SUSE Linux
Enterprise Server (SLES) 12 for which we previously built RPM packages
have now reached the end of their standard LTS (Long-Term Support)
periods, and so future releases of the Git LFS client will no longer
build packages for them.

We therefore removed the Dockerfile we used to build packages for the
RHEL/CentOS 7 and SLES 12 platforms in commit
git-lfs/build-dockers@cfde130 of
PR git-lfs/build-dockers#71.  As well, in a prior commit in this PR
we removed the entries for these platforms from the list of our
supported Linux distribution versions in the DistroMap Ruby class
source file, which is utilized by several scripts run by our GitHub
Actions CI and release workflow jobs.

Since our CI and release workflows will no longer run on any platforms
where libcurl is linked against the legacy libnss3 library, we can now
also remove the checks for the libnss3 library from our t/t-clone.sh
test script.

Author: chrisd8088

t/t-clone.sh

@@ -4,13 +4,6 @@
 
 ensure_git_version_isnt $VERSION_LOWER "2.2.0"
 
-# Check for a libnss3 dependency in Git until we drop support for CentOS 7.
-GIT_LIBNSS=0
-if [ "$IS_WINDOWS" -eq 0 -a "$IS_MAC" -eq 0 ]; then
-  GIT_LIBNSS="$(ldd "$(git --exec-path)"/git-remote-https | grep -c '^\s*libnss3\.' || true)"
-fi
-export GIT_LIBNSS
-
 export CREDSDIR="$REMOTEDIR/creds-clone"
 setup_creds
 
@@ -121,11 +114,6 @@ begin_test "cloneSSL"
 (
   set -e
 
-  if [ "$GIT_LIBNSS" -eq 1 ]; then
-    echo "skip: libnss does not support the Go httptest server certificate"
-    exit 0
-  fi
-
   if [ "$IS_WINDOWS" -eq 1 ]; then
     git config --global "http.sslBackend" "openssl"
   fi
@@ -205,11 +193,6 @@ begin_test "clone ClientCert"
 (
   set -e
 
-  if [ "$GIT_LIBNSS" -eq 1 ]; then
-    echo "skip: libnss does not support the Go httptest server certificate"
-    exit 0
-  fi
-
   if [ "$IS_WINDOWS" -eq 1 ]; then
     git config --global "http.sslBackend" "openssl"
   fi
@@ -330,11 +313,6 @@ begin_test "clone ClientCert with homedir certs"
 (
   set -e
 
-  if [ "$GIT_LIBNSS" -eq 1 ]; then
-    echo "skip: libnss does not support the Go httptest server certificate"
-    exit 0
-  fi
-
   if [ "$IS_WINDOWS" -eq 1 ]; then
     git config --global "http.sslBackend" "openssl"
   fi