Remove vectors: Boolean expressions do not require signed bitvectors

[tautschnig]

Any bitvector type will do as all we need to produce is a constant with all bits set (see
https://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html: "Vectors are compared element-wise producing 0 when comparison is false and -1 (constant of the appropriate type where all bits are set) otherwise.").

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• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
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[kroening]

The from_integer(-1, subtype); works on unsigned bitvectors as well (it's designed to), so dropping the precondition may be the right thing to do.

[codecov]

Codecov Report

Base: 77.99% // Head: 77.99% // Decreases project coverage by -0.00% ⚠️

Coverage data is based on head (9baef8f) compared to base (f8e6230).
Patch coverage: 94.20% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #7234      +/-   ##
===========================================
- Coverage    77.99%   77.99%   -0.01%     
===========================================
  Files         1619     1619              
  Lines       187185   187184       -1     
===========================================
- Hits        146000   145999       -1     
  Misses       41185    41185              

Impacted Files	Coverage Δ
...src/java_bytecode/java_bytecode_convert_method.cpp	97.69% <ø> (ø)
jbmc/src/java_bytecode/java_bytecode_language.cpp	92.81% <ø> (ø)
jbmc/src/java_bytecode/java_string_literals.cpp	94.54% <ø> (ø)
jbmc/unit/java-testing-utils/require_type.cpp	92.18% <75.00%> (ø)
jbmc/src/java_bytecode/java_types.cpp	95.13% <88.46%> (ø)
jbmc/src/java_bytecode/assignments_from_json.cpp	97.28% <100.00%> (ø)
.../src/java_bytecode/java_bytecode_convert_class.cpp	94.18% <100.00%> (ø)
...src/java_bytecode/java_bytecode_typecheck_expr.cpp	100.00% <100.00%> (ø)
...src/java_bytecode/java_bytecode_typecheck_type.cpp	96.00% <100.00%> (ø)
jbmc/src/java_bytecode/java_object_factory.cpp	94.40% <100.00%> (ø)
... and 15 more

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[tautschnig]

The from_integer(-1, subtype); works on unsigned bitvectors as well (it's designed to), so dropping the precondition may be the right thing to do.

Done.