Changes

[lldb][NFC] Remove unused ExpressionParser::Parse
Summary: This function is only used internally by ClangExpressionParser.
By putting it in the ExpressionParser class all languages that implement
ExpressionParser::Parse have to share the same signature (which forces
us in downstream to add swift-specific arguments to
ExpressionParser::Parse which then propagate to ClangExpressionParser
and so on).
Reviewers: davide
Subscribers: JDevlieghere, lldb-commits
Tags: #upstreaming_lldb_s_downstream_patches, #lldb
Differential Revision: https://reviews.llvm.org/D69710