[Android templates] Remove jetifier usage (flutter#173431)

Fixes flutter#173430

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- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
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- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
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Fixes] where supported.
- [x] All existing and new tests are passing.

Author: reidbaker

packages/flutter_tools/templates/app/android.tmpl/gradle.properties.tmpl

@@ -1,3 +1,2 @@
 org.gradle.jvmargs=-Xmx8G -XX:MaxMetaspaceSize=4G -XX:ReservedCodeCacheSize=512m -XX:+HeapDumpOnOutOfMemoryError
 android.useAndroidX=true
-android.enableJetifier=true

packages/flutter_tools/templates/module/android/gradle/gradle.properties.tmpl

@@ -1,3 +1,2 @@
 org.gradle.jvmargs=-Xmx8G -XX:MaxMetaspaceSize=4G -XX:ReservedCodeCacheSize=512m -XX:+HeapDumpOnOutOfMemoryError
 android.useAndroidX=true
-android.enableJetifier=true