The interpreter is not used for debugging any more. Hence any breakpoint
support and related functionality is dead code.

This CL removes
- the {SetBreakpoint} and {GetBreakpoint} methods,
- the {break_pc_} field which holds the current pause position,
- the {break_flags_} field which is used to break at function entry and
  after calls,
- functions to modify {break_flags_},
- the dead {kInternalBreakpoint} and {kInvalidPc} constants (plus
  respective macros and enums),
- the {orig_start} and {orig_end} fields (code is not being modified any
  more, so we just use {start} and {end} now),
- the {PrepareStepIn} method,
- the unimplemented {SetTracing} method, and
- two tests that test breakpoints in the interpreter.

R=thibaudm@chromium.org

Bug: v8:10389
Change-Id: I52103c37516446e40d3dfa365d6b480a7c623577
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2215163
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67958}