Factor out licence stripping
Factor out licence stripping

Matches code in Blockly Games.
No functional change.

google/blockly,mark-friedman/blockly,joshlory/blockly,rachel-fenichel/blockly,mark-friedman/blockly,google/blockly,joshlory/blockly,nickmain/blockly,rachel-fenichel/blockly,google/blockly,nickmain/blockly,rachel-fenichel/blockly,mark-friedman/blockly,rachel-fenichel/blockly,google/blockly,picklesrus/blockly,google/blockly,nickmain/blockly,google/blockly,nickmain/blockly,google/blockly,rachel-fenichel/blockly,nickmain/blockly,mark-friedman/blockly,picklesrus/blockly,mark-friedman/blockly,rachel-fenichel/blockly,mark-friedman/blockly,nickmain/blockly,joshlory/blockly,rachel-fenichel/blockly,picklesrus/blockly