BUILDING.txt should not encourage to activate docs profile on building binary artifacts

`$ mvn package -Pdist,native,docs -DskipTests -Dtar`
`$ mvn package -Pdist,native,docs,src -DskipTests -Dtar`

[INFO] -------< org.apache.hadoop:hadoop-client-check-test-invariants >--------
[INFO] Building Apache Hadoop Client Packaging Invariants for Test 3.4.0-SNAPSHOT [105/112]
[INFO] --------------------------------[ pom ]---------------------------------

...

[INFO] --- maven-enforcer-plugin:3.0.0-M1:enforce (enforce-banned-dependencies) @ hadoop-client-check-test-invariants ---
[INFO] Adding ignorable dependency: org.apache.hadoop:hadoop-annotations:null
[INFO]   Adding ignore: *
[WARNING] Rule 1: org.apache.maven.plugins.enforcer.BanDuplicateClasses failed with message:
Duplicate classes found:

  Found in:
    org.apache.hadoop:hadoop-client-minicluster:jar:3.4.0-SNAPSHOT:compile
    org.apache.hadoop:hadoop-client-runtime:jar:3.4.0-SNAPSHOT:compile
  Duplicate classes:
    org/apache/hadoop/shaded/org/apache/xerces/impl/dv/dtd/NMTOKENDatatypeValidator.class
    org/apache/hadoop/shaded/org/apache/xerces/dom/DOMImplementationListImpl.class

...

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-enforcer-plugin:3.0.0-M1:enforce (enforce-banned-dependencies) on project hadoop-client-check-test-invariants: Some Enforcer rules have failed. Look above for specific messages explaining why the rule failed. -> [Help 1]