Update "Upgrading From" section to use "2.x"

Author: izeye

spring-boot-project/spring-boot-docs/src/docs/antora/modules/ROOT/pages/documentation.adoc

@@ -25,7 +25,7 @@ You should always ensure that you are running a {url-github-wiki}/Supported-Vers
 
 Depending on the version that you are upgrading to, you can find some additional tips here:
 
-* *From 1.x:* xref:upgrading.adoc#upgrading.from-1x[Upgrading from 1.x]
+* *From 2.x:* xref:upgrading.adoc#upgrading.from-2x[Upgrading from 2.x]
 * *To a new feature release:* xref:upgrading.adoc#upgrading.to-feature[Upgrading to New Feature Release]
 * *Spring Boot CLI:* xref:upgrading.adoc#upgrading.cli[Upgrading the Spring Boot CLI]
 

spring-boot-project/spring-boot-docs/src/docs/antora/modules/ROOT/pages/redirect.adoc

@@ -78,7 +78,6 @@
 * xref:ROOT:upgrading.adoc#upgrading[#upgrading]
 * xref:ROOT:upgrading.adoc#upgrading[#getting-started-upgrading-from-an-earlier-version]
 * xref:ROOT:upgrading.adoc#upgrading.cli[#upgrading.cli]
-* xref:ROOT:upgrading.adoc#upgrading.from-1x[#upgrading.from-1x]
 * xref:ROOT:upgrading.adoc#upgrading.to-feature[#upgrading.to-feature]
 * xref:api:rest/actuator/auditevents.adoc#audit-events[actuator-api#audit-events]
 * xref:api:rest/actuator/auditevents.adoc#audit-events.retrieving[actuator-api#audit-events.retrieving]

spring-boot-project/spring-boot-docs/src/docs/antora/modules/ROOT/pages/upgrading.adoc

@@ -9,10 +9,10 @@ If you are more than one release behind, please make sure that you also review t
 
 
 
-[[upgrading.from-1x]]
-== Upgrading From 1.x
+[[upgrading.from-2x]]
+== Upgrading From 2.x
 
-If you are upgrading from the `1.x` release of Spring Boot, check the {url-github-wiki}/Spring-Boot-2.0-Migration-Guide[migration guide] on the project wiki that provides detailed upgrade instructions.
+If you are upgrading from the `2.x` release of Spring Boot, check the {url-github-wiki}/Spring-Boot-3.0-Migration-Guide[migration guide] on the project wiki that provides detailed upgrade instructions.
 Check also the {url-github-wiki}[release notes] for a list of "`new and noteworthy`" features for each release.