Remove incorrect UTF decode assert (#5028)

The assert assumed that after removing a BOM and "deflating"
UTF* to UTF8, the decoded (UTF8) size should be less than
the raw size (UTF8 or UTF16). However, UTF8 is not actually
smaller than UTF16 for some UTF16 codepoints. Specifically,
UTF16 code points (2 bytes) 0x800+ are 3 to 4 bytes large.

The assert is mostly obeyed for source code files, but is
easily violated for binary files with more random values.

Wikipedia clarifies why:

https://en.wikipedia.org/wiki/UTF-8#UTF-16

"Text encoded in UTF-8 will be smaller than the same text encoded
in UTF-16 if there are more code points below U+0080 than in the range
U+0800..U+FFFF. This is true for all modern European languages. It is
often true even for languages like Chinese, due to the large number of
spaces, newlines, digits, and HTML markup in typical files."

source/compiler-core/slang-source-loc.cpp

@@ -597,7 +597,6 @@ void SourceFile::setContents(ISlangBlob* blob)
 
     char const* decodedContentBegin = (char const*)m_contentBlob->getBufferPointer();
     const UInt decodedContentSize = m_contentBlob->getBufferSize();
-    assert(decodedContentSize <= rawContentSize);
     char const* decodedContentEnd = decodedContentBegin + decodedContentSize;
 
     m_content = UnownedStringSlice(decodedContentBegin, decodedContentEnd);