Fix #3886 and #3887: drop remaining KitKat TODOs. (#5018)

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## Explanation
This PR fixes #3886 and fixes #3887 by dropping TODOs for those obsolete
issues so that they can be fully closed.

## Essential Checklist
<!-- Please tick the relevant boxes by putting an "x" in them. -->
- [ ] The PR title and explanation each start with "Fix #bugnum: " (If
this PR fixes part of an issue, prefix the title with "Fix part of
#bugnum: ...".)
- [x] Any changes to
[scripts/assets](https://github.com/oppia/oppia-android/tree/develop/scripts/assets)
files have their rationale included in the PR explanation.
- [x] The PR follows the [style
guide](https://github.com/oppia/oppia-android/wiki/Coding-style-guide).
- [x] The PR does not contain any unnecessary code changes from Android
Studio
([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#undo-unnecessary-changes)).
- [x] The PR is made from a branch that's **not** called "develop" and
is up-to-date with "develop".
- [x] The PR is **assigned** to the appropriate reviewers
([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#clarification-regarding-assignees-and-reviewers-section)).

build_flavors.bzl

@@ -92,7 +92,7 @@ _FLAVOR_METADATA = {
         "target_sdk_version": 31,
         "multidex": "manual_main_dex",
         "main_dex_list": _MAIN_DEX_LIST_TARGET_KITKAT,
-        "proguard_specs": [],  # TODO(#3886): Re-add Proguard support to alpha_kitkat.
+        "proguard_specs": [],
         "production_release": True,
         "deps": [
             "//app/src/main/java/org/oppia/android/app/application/alpha:alpha_application",

utility/src/main/java/org/oppia/android/util/parser/image/GlideImageLoader.kt

@@ -65,7 +65,6 @@ class GlideImageLoader @Inject constructor(
     target: ImageTarget<Drawable>,
     transformations: List<ImageTransformation>
   ) {
-    // TODO(#3887): Investigate why this has a native crash on KitKat & find a fix.
     glide
       .asDrawable()
       .load(imageDrawableResId)