[birt-dev]CheckIn: Fix Bugzilla Bug 156974 --- Remove deprecated method

["Wei Zhao (Shang)" <wei.zhao@xxxxxxxxxxx>]

Title: [birt-dev]CheckIn: Fix Bugzilla Bug 156974 --- Remove deprecated method from reportContext

- Summary:
Remove deprecated API getConfigVariableValue in IReportContext.

- Bugzilla Bug (s) Resolved:
Fix Bugzilla Bug 156974 --- Remove deprecated method from reportContext

- Description:
Since getConfigVariableValue in IReportContext has been deprecated and always return null, remove it.

- Tests Description  :
Manual Test.

- Notes to Build Team:

- Notes to Developers:

- Notes to QA:  
 
- Notes to Documentation:  

- Files Edited:
"/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/script/IReportContext.java"
"/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/script/internal/ReportContextImpl.java"

- Files Added:

- Files Deleted

-Wei Zhao( Shanghai )