Bug 1849329 - Update local GV docs

We do not need to patch the build system to read the GeckoView version anymore.

docs/substituting-local-gv.md

@@ -1,26 +1,8 @@
 # Substituting local GeckoView
 
 ### 1. Manually publish local GeckoView to local Maven
-First, to get the version that we are locally publishing (which will be used in later steps) please add the following:
 
-*geckoview/build.gradle*
-```diff
-diff --git a/mobile/android/geckoview/build.gradle b/mobile/android/geckoview/build.gradle
-index 731026796921b..81cc6782be291 100644
---- a/mobile/android/geckoview/build.gradle
-+++ b/mobile/android/geckoview/build.gradle
-@@ -398,6 +398,7 @@ android.libraryVariants.all { variant ->
- apply plugin: 'maven-publish'
- 
- version = getVersionNumber()
-+println("version = " + version)
- group = 'org.mozilla.geckoview'
- 
- def getArtifactId() {
-
-```
-
-We can now publish our local GeckoView to our local maven.
+Publish our local GeckoView to our local maven:
 ```sh
 ./mach build && ./mach gradle \
     geckoview:publishWithGeckoBinariesDebugPublicationToMavenLocal \
@@ -29,7 +11,7 @@ We can now publish our local GeckoView to our local maven.
 
 :warning: **This needs to be run every time you make changes.** :warning:
 
-You need to copy the version in the logs or run 
+You need to copy the version in the logs or run:
 ```sh
 ./mach build | grep version
 ```