t: align missing object push test deletion steps

Our t/t-pre-push.sh and t/t-push-failures-local.sh test scripts include
a number of tests which validate the behaviour of the "git lfs pre-push"
and "git push" commands when Git LFS objects are missing or corrupt.

While these tests are largely similar in their implementation, they
vary in a number of formatting and implementation details unrelated to
the specifics of the different conditions they simulate.  These
variations are artifacts of the evolution of our test suite over time;
for example, the tests in the t/t-push-failures-local.sh script were
refactored and collected from several earlier tests in commit
4d52e08 of PR git-lfs#3109, and the original
versions of the tests in the t/t-pre-push.sh script were added
incrementally in PRs git-lfs#447, git-lfs#2199, and git-lfs#2574.

In a subsequent commit in this PR we expect to update the Git LFS
client to remove some non-functional code which attempts to recreate
missing Git LFS objects during push operations.  In many cases this
change will cause the client to report missing objects in an earlier
stage of push operations than it does now.  We also expect to reword
the error message the client will output in such cases.

Before we make these changes, we first revise the related tests in our
test suite so they are as simple and similar as possible.  This will
ensure that when we update the Git LFS client we can clearly identify
the changes that we need to make in our tests to accommodate the
client's new behaviour.

In a pair of tests in t/t-pre-push.sh script, and in another pair of
tests in the t/t-push-failures-local.sh script, the tests' initial
setup code creates several Git LFS objects and then removes the object
file in the .git/lfs/objects directory hierarchy for one of them.

In each case, we can replace this code with a simple call to our
delete_local_object() test helper function, which performs the
equivalent action of removing an object's file from the internal
Git LFS storage directories.

Author: chrisd8088

t/t-pre-push.sh

@@ -387,11 +387,7 @@ begin_test "pre-push with missing and present pointers (lfs.allowincompletepush
   git rm missing.dat
   git commit -m "remove missing"
 
-  # :fire: the "missing" object
-  missing_oid_part_1="$(echo "$missing_oid" | cut -b 1-2)"
-  missing_oid_part_2="$(echo "$missing_oid" | cut -b 3-4)"
-  missing_oid_path=".git/lfs/objects/$missing_oid_part_1/$missing_oid_part_2/$missing_oid"
-  rm "$missing_oid_path"
+  delete_local_object "$missing_oid"
 
   git config lfs.allowincompletepush true
 
@@ -438,11 +434,7 @@ begin_test "pre-push reject missing pointers (lfs.allowincompletepush default)"
   git rm missing.dat
   git commit -m "remove missing"
 
-  # :fire: the "missing" object
-  missing_oid_part_1="$(echo "$missing_oid" | cut -b 1-2)"
-  missing_oid_part_2="$(echo "$missing_oid" | cut -b 3-4)"
-  missing_oid_path=".git/lfs/objects/$missing_oid_part_1/$missing_oid_part_2/$missing_oid"
-  rm "$missing_oid_path"
+  delete_local_object "$missing_oid"
 
   echo "refs/heads/main main refs/heads/main 0000000000000000000000000000000000000000" |
     git lfs pre-push origin "$GITSERVER/$reponame" 2>&1 |

t/t-push-failures-local.sh

@@ -28,11 +28,7 @@ begin_test "push with missing objects (lfs.allowincompletepush true)"
   git rm missing.dat
   git commit -m "remove missing"
 
-  # :fire: the "missing" object
-  missing_oid_part_1="$(echo "$missing_oid" | cut -b 1-2)"
-  missing_oid_part_2="$(echo "$missing_oid" | cut -b 3-4)"
-  missing_oid_path=".git/lfs/objects/$missing_oid_part_1/$missing_oid_part_2/$missing_oid"
-  rm "$missing_oid_path"
+  delete_local_object "$missing_oid"
 
   git config lfs.allowincompletepush true
 
@@ -76,11 +72,7 @@ begin_test "push reject missing objects (lfs.allowincompletepush false)"
   git rm missing.dat
   git commit -m "remove missing"
 
-  # :fire: the "missing" object
-  missing_oid_part_1="$(echo "$missing_oid" | cut -b 1-2)"
-  missing_oid_part_2="$(echo "$missing_oid" | cut -b 3-4)"
-  missing_oid_path=".git/lfs/objects/$missing_oid_part_1/$missing_oid_part_2/$missing_oid"
-  rm "$missing_oid_path"
+  delete_local_object "$missing_oid"
 
   git config lfs.allowincompletepush false