[MNG-7189] Remove undocumented environment variable MAVEN_BASEDIR in startup scripts

This closes #490

apache-maven/src/assembly/shared/init

@@ -114,7 +114,7 @@ concat_lines() {
   fi
 }
 
-MAVEN_PROJECTBASEDIR="${MAVEN_BASEDIR:-`find_maven_basedir "$@"`}"
+MAVEN_PROJECTBASEDIR="`find_maven_basedir "$@"`"
 MAVEN_OPTS="`concat_lines "$MAVEN_PROJECTBASEDIR/.mvn/jvm.config"` $MAVEN_OPTS"
 
 # For Cygwin, switch project base directory path to Windows format before

apache-maven/src/assembly/shared/init.cmd

@@ -7,9 +7,6 @@ set MAVEN_CMD_LINE_ARGS=%*
 @REM Find the project basedir, i.e., the directory that contains the directory ".mvn".
 @REM Fallback to current working directory if not found.
 
-set "MAVEN_PROJECTBASEDIR=%MAVEN_BASEDIR%"
-if not "%MAVEN_PROJECTBASEDIR%"=="" goto endDetectBaseDir
-
 set "EXEC_DIR=%CD%"
 set "WDIR=%EXEC_DIR%"