Deps: Remove kotlinx coroutines from app

These unused dependencies got added to this module via this
(56a0534) commit, which amongst
other changes, moved the media placeholders into it's own module.
However, these dependencies never got to be used and as such can be
safely removed.

------------------------------------------------------------------------

This removal was suggested by the dependency analysis report, see below:

Advice for :app
Unused dependencies which should be removed:
  implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.4'
  ...

Dependencies which should be removed or changed to runtime-only:
  runtimeOnly 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.6.4'
   (was implementation)

Author: ParaskP7

app/build.gradle

@@ -47,9 +47,6 @@ dependencies {
     implementation project(':wordpress-shortcodes')
     implementation project(':media-placeholders')
 
-    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$kotlinCoroutinesVersion"
-    implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$kotlinCoroutinesVersion"
-
     implementation 'androidx.appcompat:appcompat:1.0.0'
     implementation "org.wordpress:utils:$wordpressUtilsVersion"