STYLE: simplify string handling for expansions in primitiveEntry

src/OpenFOAM/db/dictionary/dictionaryEntry/dictionaryEntry.H

...M/db/dictionary/dictionaryListEntry/dictionaryListEntry.H

src/OpenFOAM/db/dictionary/entry/entry.H

src/OpenFOAM/db/dictionary/entry/entryIO.C

src/OpenFOAM/db/dictionary/primitiveEntry/primitiveEntry.C

src/OpenFOAM/db/dictionary/primitiveEntry/primitiveEntry.H

src/OpenFOAM/db/dictionary/primitiveEntry/primitiveEntryIO.C

...AM/db/dictionary/primitiveEntry/primitiveEntryTemplates.C